María Abelenda

Hematology and blood chemistry of wintering common cranes

We studied the hematology and blood chemistry of wintering Common Cranes (Grus grus). Red cell numbers (2.460 x 106 mm-3), hemoglobin content (14.8 g/100 ml), and hematocrit (42.9%) were similar in adult and young birds. Young birds have significantly higher leukocyte numbers (28 x 103 mm-3) than adults (22 x 103 mm-3). Heterophils are the most abundant white blood cells in adults (55%) whereas young have the same proportion of heterophils and lymphocytes (47%). Plasma protein levels are similar in young and adult birds (4.9 g/100 ml), as is the plasma cholesterol level (200 mg/100 ml). However, adults have higher plasma urea levels and lower uric acid and plasma triglyceride levels than young birds (7.1 vs. 5.5 mg/100 ml, 2.9 vs. 4.4 mg/100 ml, and 81 vs. 110 mg/100 ml, respectively).

Inhibition of diet-induced thermogenesis during pregnancy in the rat

Both virgin and pregnant rats were maintained at two different ambient temperatures (28° C and 10° C) for 19 days. Virgin rats maintained their daily food intake and body weight at both temperatures. At 28° C pregnant rats showed a greater daily food intake and body weight than virgin ones and their brown adipose tissue suffered regressive changes in composition when compared with brown fat of virgin rats. At 10° C the increases in daily food intake and body weight of pregnant rats took place from day 15–16 of pregnancy onward and foetuses taken from these pregnant rats were smaller than those taken from pregnant rats at 28° C. It is concluded that pregnant rats at thermoneutrality, although hyperphagic, do not show diet-induced thermogenesis. However, it is proposed that pregnant rats in the cold may show BAT cold-induced thermogenesis.

Inactivation of brown adipose tissue thermogenesis by oestradiol treatment in cold-acclimated rats

Both cold-acclimated female rats and rats at thermoneutrality received 0.15–0.20 mg daily of 17β-oestradiol over 15 days via a Silastic capsule implanted subcutaneously. Controls received empty implants. Comparison between the oestradiol-treated animals and the untreated controls revealed that at thermoneutrality, oestradiol treatment decreased food intage and body weight gain, but did not affect brown adipose tissue (BAT) thermogenesis and composition. By contrast, in cold-acclimated rats, oestradiol treatment did not modify food intake or body weight gain, but it decreased BAT thermogenesis. It is concluded that the effects of oestradiol treatment on BAT depend on the activity of the tissue, i.e. it has no effect on BAT when the tissue is thermogenically inactive, but it decreases cold-induced BAT thermogenesis. It is suggested that oestradiol could be the hormonal factor responsible for the previously observed inactivation of BAT thermogenesis during pregnancy in cold-acclimated rats.

Dissociation between brown adipose tissue thermogenesis and sympathetic activity in rats with high plasma levels of oestradiol

It has been shown previously that high plasma levels of oestradiol inhibit brown adipose tissue thermogenesis. Since rats and mice show a close association between thermogenic activity in and sympathetic discharge to brown fat, we measured the noradrenaline turnover in rats with high plasma levels of oestradiol to establish whether the observed inhibition of thermogenic activity is brought about by a reduction in the sympathetic drive to brown adipocytes. Oestradiol-filled Silastic capsules were implanted subcutaneously in female rats previously acclimated either to thermoneutrality or to cold. Control rats received empty implants. After 15 days treatment, noradrenaline turnover was measured by blocking its synthesis with α-methyl-p-tyrosine. As expected, noradrenaline turnover was higher in cold-acclimated rats than in rats kept at thermoneutrality. The presence of high plasma oestradiol levels did not alter sympathetic activity in any of the treated groups despite reducing thermogenic activity. This result reveals that oestradiol dissociates the thermogenic activity of brown adipose tissue from its sympathetic activation. Such dissociation has never been previously reported in rats, although it seems to be common in Syrian hamsters. However the causative factor in this species is unknown.

Cold-induced and diet-induced thermogenesis in progesterone-treated rats

Both cold-acclimated rats and rats at thermoneutrality received 1.5 mg/day of progesterone over a period of 15 days by means of two subcutaneously implanted Silastic capsules. Progesterone treatment increased total food intake and body mass gain in both groups of treated animals when compared with their controls at the same ambient temperature. However, the interscapular brown adipose tissue (BAT) of the treated rats showed the same thermogenic activity (assessed by GDP-binding), mass and gross composition as that of their respective controls. If it is assumed that enhanced food intake is the physiological drive for diet-induced thermogenesis, it could be concluded that progesterone inhibits diet-induced thermogenesis at thermoneutrality, but has no effect in cold-induced thermogenesis. However, if the physiological drive for diet-induced thermogenesis is not enhanced food intake, but an imbalance in the diet, then given that the same diet was offered to all animals thoroughout the experimental period, it could be that progesterone does not affect BAT, either at thermoneutrality or in the cold.

Adiponectin values are unchanged during pregnancy in rats

Adiponectin is believed to be a key factor in determining insulin sensitivity. In turn, insulin sensitivity is known to change from an enhanced state in early pregnancy to a reduced one in late pregnancy. A role for adiponectin in these changes has been proposed for mice but questioned for humans. We addressed this issue in rats by measuring adiponectin expression in both visceral and subcutaneous white adipose tissue, together with tissue content and release of the hormone in non-pregnant and in pregnant rats by days 8, 15 and 19 of pregnancy. Plasma concentration was also determined. No differences were found in any of the parameters measured between non-pregnant and pregnant rats at any time of pregnancy despite changes in white adipose tissue mass and insulin sensitivity. Adiponectin was also detected in cerebrospinal fluid at a concentration 1,000 times lower than in plasma, but again no differences were found between non-pregnant and pregnant animals. It is concluded that adiponectin does not play any role in regulating changes in insulin sensitivity during pregnancy in rats.

Cold-induced thermogenesis in hypothyroid rats

Hypothyroidism was induced in adult rats by oral administration of methimazole. Euthyroid and hypothyroid rats were maintained at 23 °C or exposed at 6 °C for 3 weeks. Both euthyroid and hypothyroid rats maintained at 23 °C had similar interscapular brown adipose tissue (BAT) composition and thermogenic activity. Cold-exposed hypothyroid rats showed the same interscapular BAT mass and gross tissue composition as cold-exposed euthyroid animals, but the interscapular BAT of cold-exposed hypothyroid rats did not show the characteristic increase in GDP binding, and the increase in mitochondrial mass was lower than in euthyroid rats. From these results we conclude that thyroid hormones do not influence BAT significantly when thermogenic requirements are moderate, but they participate in the trophic response of the tissue when thermogenic requirements are intense. This thyroid hormone participation in the BAT trophic response occurs at the mitochondrial level, both in quantitative (mitochondrial mass) and qualitative (GDP-binding) aspects.

Haematology and Plasma Chemistry of Male Lizards, Psammodromus algirus. Effects of Testosterone Treatment

This study deals with a general description of haematology and plasma chemistry of free-living males of the lacertid lizards Psammodromus algirus subjected to an experiment of testosterone supplementation. In control lizards the number of red blood cells — 1700000 cells/µl — was smaller than those published for birds and mammals. Haematocrit and haemoglobin content were 33% and 8.4 g/dl. However, they were greater than those reported for other lizards. Testosterone treatment reduced the number of red blood cells and haemoglobin content but did not affect red cell indexes. White blood cell number was 27 000 cells/µl, a value higher than those previously published for other lizards. Lymphocytes, heterophils and azurophils counts were 22300, 3700 and 2000 cells/µl. Monocytes, eosinophils and basophils showed proportions lower than 500 cell/µl. Testosterone treatment reduced the total number of leucocytes (17000 cells/µl) and the number of lymphocytes (10000 cell/µl). Glucose plasma level was in the range published for birds — 250 mg/dl — in both control and treated lizards. Plasma proteins (3.6 g/dl), uric acid and urea (4.5 and 5.4 mg/dl, respectively) were similar to previously published values in lizards. Testosterone treatment increased only protein levels (8.2 g/dl).

Leptin release is decreased in white adipocytes isolated from progesterone-treated rats.

Previously, it has been proposed that progesterone has an inhibitory effect on leptin secretion by white adipocytes, because female rats treated with progesterone show unchanged plasma leptin concentrations despite heavier fat depots. In this study, we show that adipocytes isolated from intact rats release the same amount of leptin either in the presence or the absence of progesterone in the incubation medium. However, when we isolated white adipocytes from progesterone‐treated and sham‐treated rats and measured their leptin release for 6 hr, we found that adipocytes isolated from rats treated with progesterone for 72 hr showed a lower leptin release than those of sham‐treated rats. These results confirm the proposed inhibitory action of progesterone on leptin production.

Oxygen consumption of oestradiol-treated rats

Rectal temperature and oxygen consumption (üüO2) were monitored in female rats acclimated either to cold or to thermoneutrality and with and without chronic administration of oestradiol. The hormone is known to inactivate brown adipose tissue (BAT) and to reduce its response to noradrenaline (NA). The role of sympathetic control was studied by administering NA or the adrenergic blocker propranolol. Oestradiol treatment did not affect rectal temperature in the states of acclimation to thermoneutrality and to cold, nor did it change the hypothermic response of cold-exposed rats to temporary food deprivation. In the cold-acclimated rats, both controls and oestradiol-treated animals exhibited similar degrees of metabolic reduction after propranolol administration in the cold and similar degrees of metabolic activation by NA at thermoneutrality. Rats acclimated to thermoneutrality showed a larger metabolic response to NA when treated with oestradiol. The results suggest that oestradiol, while inactivating the BAT response to NA, activates the NA responsiveness of other metabolically active tissues in cold-induced thermogenesis. The observation of a greater oxidative capacity in the kidney and the rectus abdominis muscle of oestradiol-treated, cold-acclimated rats would be in line with this proposal.