Jutta Gottschalk

Possible Role of Dexamethasone in Sensitizing the Beta-2-Adrenergic Receptor System in vivo in Calves during Concomitant Treatment with Clenbuterol

β2-Agonists blunt the function of the β-adrenoceptor G-protein adenylate cyclase-signalling system, whereas glucocorticoids reverse the agonist-mediated diminished β-adrenergic responses; however, these effects have not been reported in vivo in calf lymphocytes. In this study, we first investigated the presence of the β2-adrenergic receptors on calf lymphocytes, and second we tested the effects of either clenbuterol alone or in combination with dexamethasone on receptor expression and function (isoproterenol-induced intracellular adenosine 3′,5′-cyclic monophosphate (cAMP) formation) in vivo. (–)-[125I]-Iodocyanopindolol (ICYP) binding to intact calf lymphocytes was rapid, saturable (maximal number of binding sites 987 ± 89 ICYP-binding sites/cell, n = 4) and of high affinity (KD value 17.23 ± 2.8 pmol/l, n = 4). These binding sites were of the β2-subtypes of adrenoceptors as indicated by the fact that β-agonists inhibited ICYP binding with an order of potency: (–)-isoproterenol > (–)-adrenaline > (–)-noradrenaline. Furthermore, the selective β2-adrenoceptor antagonist ICI 118.551 was about >1,500 times more potent in inhibiting ICYP binding than was the β1-selective adrenoceptor antagonist CGP 20712A. Consequently, calves were treated with clenbuterol (1.0 µg/kg b.i.d., i.v.) for 9 days alone or simultaneously with dexamethasone (0.1 mg/kg, i.v., once a day for 4 days). Clenbuterol decreased the number of lymphocyte β2-adrenergic receptors by about 40–50% after only 48 h of drug administration. This was accompanied by a decrement in isoproterenol-induced lymphocyte cAMP formation. Upon application of both drugs, dexamethasone restored the clenbuterol-mediated decrease in β2-adrenoceptors and cAMP production. Dexamethasone elevated the number of β2-adrenoceptors and cAMP almost 1.5- to 2-fold at 24 h of drug administration, an effect that persisted for up to 24 h following drug withdrawal. Neither clenbuterol nor the combination with dexamethasone had an influence on the affinity of the receptor for the ligand. The present results demonstrate that dexamethasone in vivo upregulates the number and function of calf lymphocyte β2-adrenoceptors, and thus enhances the sensitivity of the β2-adrenoceptor signal-transduction pathway for clenbuterol during concomitant treatment with both drugs.

Influence of topical dexamethasone applications on insulin, glucose, thyroid hormone and cortisol levels in dogs

The influence of two topical dexamethasone applications (dermal and ototopical) on plasma insulin, glucose, thyroid hormone and cortisol levels was investigated in beagle dogs. Both treatments significantly decreased basal cortisol values, associated with exaggerated rise in insulin (approximately 50%), together with unchanged serum glucose levels. Dermal dexamethasone quickly decreased plasma thyroxin (T4) levels; whereas dexamethasone in ear drops gradually inhibited time-dependently T4 release (18-50%). Both formulations blunted plasma triiodothyronine (T3) levels but the response induced by dermal dexamethasone was stronger than by dexamethasone ear drops. Upon drug withdrawal, insulin secretion returned to baseline a week after treatment cessation, while cortisol, T4 and T3 levels did not reach baseline values. These results suggest that topical glucocorticoids unexpectedly trigger secondary hypothyroidism with concomitant suppression of hypothalamic-pituitary-adrenal axis but sensitize the endocrine pancreas, thus, their application needs careful evaluation for surprisingly different effects on endocrine stress axis activity.

Seasonal and urban effects on the endocrinology of a wild passerine

Abstract In order to maximize their fitness, organisms in seasonal environments rely on external cues to optimally time their life‐history stages. One of the most important zeitgeber to time reproduction is the photoperiod, but further environmental cues are assessed to fine‐tune reproduction due to year‐to‐year variation in environmental conditions. However, in urbanized environments, the pervasive artificial light at night has altered the natural signal of light and darkness. Accordingly, artificial light at night was repeatedly shown to affect avian reproductive physiology and to advance seasonal reproduction in birds. However, these experiments were mainly conducted in the absence of further environmental cues to facilitate the investigation of the mechanisms which are still poorly understood. Here, we investigate whether the endocrine system of free‐ranging European blackbirds (Turdus merula) correlates with the amount of artificial light at night along a rural to urban gradient while the birds still encounter complementary environmental cues including seasonal variation in day length and temperature. Testosterone and estrone were assessed as metabolites in fecal samples and corticosterone in blood from mist‐netted blackbirds. We demonstrate that seasonal fluctuations in abiotic factors, individual conditions, but also light at night affect the reproductive and stress physiology of wild European blackbirds. Elevated artificial night light intensities were significantly positively correlated with corticosterone and negatively with female estrone levels. No effects of artificial light were found for testosterone levels. Our results suggest that female blackbirds in particular perceive even low levels of artificial light at night as a weak but chronic stressor that interacts with the hypothalamic‐pituitary‐gonadal axis and leads to a reduced secretion of reproductive hormones. These findings point out that the impacts of light pollution are diverse and we only slowly disentangle its multiple effects on physiology, ecology, and biodiversity.

Endocrine pregnancy monitoring in the two-toed sloth (Choloepus didactylus): “Pregnant or not pregnant”

Progesterone (P4), pregnanediol glucuronide (PdG), estradiol-17β (E2), and estrone sulfate (E1S) were measured in the feces of four female two-toed sloths (Choloepus didactylus) for early pregnancy diagnosis. For individual feces assignment, the examined female sloths were fed with a turquoise food colorant every second day. Fecal samples were collected one to four times per week, depending on the defecation rate throughout the pregnancies and the postpartum periods. The complete course of pregnancy was subdivided into three 16-week intervals (trimester of pregnancy, TP1-3) and a 5-week post-partum period after birth. Progesterone and PdG concentrations started to increase above luteal phase levels 3 weeks after conception (P = 0.028 and 0.005, respectively). At the beginning of TP1, P4 concentrations averaged 345.0 ± 283.0 ng/g and increased approximately 100- to 300-fold to a peak of 7588.0 ± 6717.0 ng/g over the TP3. Progesterone concentrations were considerably lower than PdG concentrations that started with 3206.0 ± 1500.0 ng/g at TP1 and increased up to 12.8556.0 ± 53.744.0 ng/g until birth. In contrast, mean concentrations of E2 (8.2 ± 2.4-11.7 ± 4.2 ng/g) and E1S (12.2 ± 6.7-22.9 ± 13.0 ng/g) elevated insignificantly and were not suitable for pregnancy detection. All hormones analyzed decreased rapidly within the first weeks after birth. Progesterone and PdG, as well as E2 and E1S, highly significantly correlated (r = 0.602, P < 0.001 and r = 0.497, P < 0.001, respectively) at TP1. During the TP2, only P4 and PdG significantly correlated (TP2: r = 0.661, P < 0.001 and postpartum period: r = 0.616, P = 0.009). In summary, only P4 metabolite concentrations were suitable to determine the status of reproduction in the two-toed sloth. Thereby, PdG was ideally suited to diagnose early pregnancy because it was more sensitive and detected pregnancy 2 weeks earlier than P4.

Luteal insufficiency in bitches as a consequence of an autoimmune response against progesterone

Shortened estrous cycles, embryonic death, and abortion might be associated with insufficient secretion of progesterone by the canine corpora lutea. The aim of this study was to investigate the concentration of progesterone, prolactin, and relaxin in hypoluteoid and control bitches during pregnancy and the nonpregnant cycle. Moreover, canine antibodies against progesterone were analyzed because of a possible connection between embryonic loss associated with hormone changes related to a hormone antibody response. An enzyme-linked immunosorbent assay (ELISA) was developed and optimized for these purposes. Serum samples from 20 short-cycling and 18 control bitches were analyzed. Animals were assigned to pregnant and nonpregnant groups after ultrasound examination. The results show that the nonpregnant, short-cycling bitches had significantly lower progesterone concentrations than the animals of the control group. In German Shepherd dogs, prolactin concentrations were significantly higher in the hypoluteoid pregnant bitches compared with the control group. Relaxin concentrations did not differ significantly between the pregnant hypoluteoid and pregnant control group at any time of measurement. Moreover, increased levels of IgE antibodies against progesterone were found in the serum of six bitches (five short-cycling bitches, one control animal) out of a total of 38 animals. The results indicated a specific binding of the antibodies to progesterone, but a cross-reaction with estradiol and testosterone might occur. The presented data verify the existence of antibodies against progesterone and suggest that these antibodies might play a role in some cases of unexplained pregnancy failure and shortened cycle length.

Characterization of the ovarian cycle in the two-toed sloths (Choloepus didactylus): An innovative, reliable, and noninvasive method using fecal hormone analyses

Little is known about reproductive physiology in the two-toed sloth (Choloepus didactylus). Therefore, the aim of this study was to obtain detailed information about the ovarian cycle. Measurements of reliable gonadal steroids in the feces of this species were undertaken. For this purpose, fecal samples were collected one to three times per week from nonpregnant captive females (n = 2) over a 16-month period. Before assay analysis, the fecal samples were extracted with methanol. Radioimmunoassays and enzyme immunoassays for fecal progesterone, estradiol-17β, pregnanediol-glucuronide (PdG), and estrone sulfate were tested for their ability to detect the ovarian activity. Using the lowest and highest progesterone values, the ovarian cycle length was comparatively analyzed. The ovarian cycle (n = 26) averaged between 31.4 ± 9.1 days (lowest progesterone) and 32.5 ± 7.5 days (highest progesterone) throughout the whole year. The length of the follicular phase, as indicated by low progesterone levels, was 18.1 ± 4.4 days (range 12-25 days), and the length of the luteal phase, as characterized by elevated progesterone levels, was 13.2 ± 1.8 days (range 11-16 days). In contrast, estradiol-17β and estrone sulfate were not suitable to detect the cycle due to irregular collection intervals. Fecal progesterone and PdG, as well as estradiol-17β and estrone sulfate, significantly correlated (r = 0.621, P < 0.01 and r = 0.606, P < 0.01). PdG concentrations (dilution factor (DF) 1:40) were considerably higher than progesterone concentrations (DF 1:10), PdG amounted in the range of 1326.7 ± 320.2 ng/g wet feces (animal S1) and 1373.8 ± 468.3 ng/g wet feces (animal S2) compared with progesterone concentrations in the range of 98.0 ± 17.0 ng/g (S1) and 105.9 ± 30.0 ng/g (S2). The estrone sulfate levels (DF 1:2) were similar to estradiol-17β (DF 1:22). The mean fecal estradiol-17β concentrations were 6.7 ± 0.9 ng/g for animal S1 and 7.5 ± 1.6 ng/g for animal S2. In conclusion, the ovarian activity of the two-toed sloth was studied using the noninvasive method by means of the fecal steroid monitoring. Progesterone was the most reliable fecal steroid hormone to determine the duration of the ovarian cycle independent of the weekly defecation rate. The course of progesterone concentrations resulted in a cycle length of 4-5 weeks length in the two-toed sloth. Thus, the reproductive activity of the two-toed sloth does not show any seasonality like the three-toed sloth.

Effects of different dosages of propylene glycol in dry cows and cows in early lactation

In this Research Paper we hypothesised that the temporary insulin resistance seen during the transition period in dairy cows may cause significant differences in the efficacy of PG at different sampling periods and that in some cases this effect will be dose dependent. Eighty four sampling sets were generated by studying 7 multiparous Holstein cows repeatedly at 4 sampling periods of 3 d length (dry cows: days 40, 39 and 38 antepartum; close up cows: days 10, 9 and 8 antepartum; fresh cows: days 3, 4 and 5 post-partum; lactating cows: days 38, 39 and 40 post-partum). On each of these days 3 h after morning feeding propylene glycol was drenched in different dosages of 100, 300 or 500 ml once per day (cross over study). The different doses were applied in an alternating order (Latin square). Blood samples were taken before, every 30 min up to 4 h, after 6 and 12 h after PG application. Following parameters have been measured: insulin, non-esterified fatty acids (NEFA), betahydroxybutyrate (BHB), bilirubin, cholesterol, potassium, aspartate aminotransferase (AST) and glutamate dehydrogenase (GLDH). Revised Quantitative Insulin Sensitivity Check Index (RQUICKI) was calculated. It was found that glucose, insulin, NEFA, BHB, bilirubin and potassium concentrations were influenced differently by the three defined dosages of propylene glycol at four different sampling periods. Whereas RQUICKI, cholesterol, AST and GLDH did not differ between the sampling periods and treatments. The major results of the study are that the effect of PG is dose-dependent and that the effect of PG is depending on the time of application according to calving. It can be concluded that in fresh cows higher dosages are necessary to provoke similar effects in comparison to dry, close up and lactating cows. Although the study did not compare to topdressing of PG from the results it is reasonable to believe that bolus application of a specific PG volume is necessary to provoke the effect.

[Progesterone and pregnanediol-glucuronid concentrations in saliva, milk and urine of female alpacas and their application in pregnancy diagnosis].

The objective of the present study was the measurement of the pregnancy associated hormones progesterone (P4) and pregnanediol-glucuronide (PdG) in saliva, milk and urine of alpacas and their potential use in pregnancy diagnosis. Sample of blood, saliva, milk and urine were obtained from 36 female alpacas before mating and throughout the pregnancy. Concentrations of P4 and PdG were determined using an enzyme immunoassay (EIA). Pregnancy was checked by ultrasonography at any sampling time. The milk samples were also tested using a commercial on-farm progesterone kit which was designed for dairy cattle. EIA-Concentrations of P4 in blood, milk and urine and urine PdG concentrations were significantly higher in pregnant than in not pregnant alpacas. There was no difference in concentrations of P4 or PdG in saliva. The accuracy of the progesterone kit was 90% for diagnosis of pregnancy and 69% for non-pregnancy. However, 70% of the false positive results also showed relatively high P4 milk concentrations in the EIA. Values of P4 in blood and PdG in urine are comparable to previous reports in alpacas and therefore can be confirmed as an indicator for pregnancy. Saliva seems unsuitable in pregnancy diagnosis in alpacas, whereas milk seems to be an adequate alternative. The use of milk and urine would simplify the pregnancy diagnosis in alpacas since in contrast to the current methods (e. g. blood progesterone) the owners can take the samples. The avoidance of blood sampling results in a considerable stress reduction for the animals. P4 measurement in milk and PdG measurement in urine are good alternatives in pregnancy diagnosis during the first month of pregnancy, when a trans-abdominal ultrasonographic examination is not yet reliable. However, since high values of P4 and PdG only show the presence of active luteal tissue and therefore are indirect markers of pregnancy the diagnosis should be confirmed using ultrasound later in pregnancy.

Feed Intake Patterns and Immediate Glycaemic and Insulinaemic Responses of Horses Following Ingestion of Different Quantities of Starch From Oat, Barley and Grains

BACKGROUND: Relevant literature indicate that more than 0.8 g starch/kg body weight from compounded feed composed of different starch sources induces disproportionate glycaemic and insulinaemic responses in horses. OBJECTIVE: It should be investigated whether crushed oats, barley and maize also cause a disproportionate increase in plasma glucose and insulin when fed as the only concentrate in quantities equal to and above 0.8 g starch/kg body weight. METHOD: Four mares received hay plus oats, barley and maize, respectively, in quantities equal to 0.8, 1.0 and 2.0 g starch/kg body weight. At the test days, chewing parameters were detected and blood sampled before and 30, 60, 90 and 120 min after the concentrate meal. Plasma glucose and insulin were measured and areas under the curve were calculated. RESULTS: Maize was ingested particularly slowly (dry matter basis; P 0.05). A defined increase in plasma glucose induced the highest insulinaemic response with oat grains. CONCLUSION: Oats and barley are ingested faster and induce higher glycaemic and insulinaemic responses than maize. Until 120 min postprandial, elevated quantities of starch from these grains seem to induce no disproportionate or at least linear increase of plasma glucose and insulin. The insulinaemic response to a defined increase of plasma glucose is particularly pronounced with oats.