W.H. Burke

Prolactin and luteinizing hormone levels in female turkeys (Meleagris gallopavo) during a photoinduced reproductive cycle and broodiness

Abstract Serum prolactin and luteinizing hormone levels were measured in female turkeys from the onset of photostimulation, through the egg-laying period and into the incubation (broodiness) phase of the reproductive cycle. Prolactin levels were low before photostimulation (22 ng/ml) and remained so during the first week of photostimulation. Levels gradually rose, reaching 45–50 ng/ml before the first ovulation. During the early laying period levels rose to 100 ng/ml or more. Seven of the ten hens studied became broody. In six of these hens there were marked increases in prolactin levels around the onset of broodiness with levels eventually reaching well over 1000 ng/ml in five of the seven hens. Hens which became broody remained so for the remainder of the experiment and their prolactin levels remained high. Three of the ten hens did not become broody, but two stopped laying during the experiment. Cessation of lay was associated with transient increases in prolactin in these individuals. LH levels increased within a few days after photostimulation and showed marked fluctuations during the ovulatory period. Levels fell at the onset of broodiness and remained low in broody hens.

Isolation and characterization of luteinizing hormone and follicle-stimulating hormone from pituitary glands of the turkey (Meleagris gallopavo)

Abstract Follicle-stimulating hormone (FSH) and luteinizing hormone (LH) were purified from the pituitary glands of the turkey (Meleagris gallopavo). These hormones were characterized biochemically and biologically and compared with chicken gonadotropins prepared in several independent laboratories. Amino acid and carbohydrate analyses demonstrated homology between turkey and other species of gonadotropin. The turkey LH purified here had significantly higher carbohydrate content than a previous preparation of turkey LH. Immunological studies further confirmed that the turkey FSH and LH were distinct from one another and that each was homologous to the respective gonadotropin from other vertebrates; the immunopotencies of the turkey hormones were similar to those from chickens. A variety of bioassays and radioreceptor assays (RRAs) confirmed the biological activity of the two turkey gonadotropins and revealed that the turkey LH was distinct from that of the chicken. As expected, the two types of turkey hormones were approximately equipotent in total gonadotropin bioassays (frog spermiation and 32P uptake by chick testes), and only the turkey LH was active in the rat Leydig cell assay and in RRA for LH in mammals. However, the turkey LH was also highly potent in several assays considered to be relatively FSH specific, including the Anolis lizard assay and several RRA systems using mammalian, turtle and avian gonadal receptors with 125I-labeled human FSH as tracer. Turkey and chicken FSH are similar in the RRAs, but the turkey LH was consistently more potent than either avian FSH in competing for FSH-binding sites. Chicken LH had relatively low activity by comparison. It is suggested that the evolution of the structure of active sites in turkey LH has involved convergence on those of the FSH molecule.

Purification of turkey prolactin and the development of a homologous radioimmunoassay for its measurement.

Prolactin has been purified from pituitary glands of the turkey (Meleagris gallopavo) and a radioimmunoassay has been developed for its measurement. The prolactin is a molecule of about 26,000 MW. It is high in glutamic and aspartic acids and in leucine, while it contains few methionine and half-cystine residues. Turkey prolactin elutes from Sephadex G-100 with a ratio of 2.0. It displays multiple bands in disc electrophoresis, when run at pH 8.3. The most prominent prolactin band is at a Rf value of 0.83–0.85. Prolactin is active in stimulating pigeon crop-sac development, but does not give a parallel dose-response to ovine prolactin. An antiserum was developed against turkey prolactin and was used to develop a homologous RIA using 125I-labeled turkey prolactin as the radioligand. The antiserum binds about 20% of the radioligand at a dilution of 1:7500. The least detectable dose of prolactin was 0.42 ± 0.13 ng when tracer and sample were simultaneously mixed with antiserum. The 50% bound point averaged 3.8 ± 0.32 ng. Considerably greater sensitivity was achieved by incubating the sample with the antiserum for 1 or 2 days prior to addition of tracer. The within-assay coefficient of variation was 7.9% for samples in the 45–65% bound range. Between-assay coefficient of variation was 8.9%. Binding is inhibited by sera from turkeys in some, but not all, stages of growth and reproductive development. Serial dilutions of sera and pituitary extracts yield dose-response curves which do not differ in slope from the purified turkey prolactin standard. Potency estimates of pituitary preparations by cropsac assay and by the prolactin RIA are in excellent agreement. Rat pituitary extract, rat prolactin, ovine prolactin, turkey FSH, LH, and GH all show no inhibition of binding even at very high doses. The antiserum neutralizes crop sac-stimulating activity of turkey prolactin.

The effects of prolactin on the gonadotropin induced rise in serum estradiol and progesterone of the laying turkey.

Abstract Mammalian LH (250 μg of NIH-LH-B9) and FSH (500 μg of FSH-P, Armour-Baldwin) elicit increases in serum estradiol (E) and progesterone (P) of laying turkeys within 30 min after a single iv injection. Prolactin (NIH-P-S11) at doses of 250 and 500 μg had no effect on the E or P levels when given in a single iv injection. One thousand micrograms of prolactin caused a significant decrease in serum E within 30 min of injection. Prolactin (500 and 1000 μg), given 30 min before LH, blocked the LH induced rise in P and at doses of 250, 500 and 1000 μg it blocked the LH induced rise in E. Five hundred and 1000 μg of prolactin blocked the FSH induced rise in P and doses of 250, 500 and 1000 μg of prolactin blocked the FSH induced rise in E. It is concluded that prolactins antigonadotropic effect is exerted, at least in part, by interfering with gonadotropin induced increases in ovarian steroid levels in the blood.

Serum levels of luteinizing hormone (LH), prolactin, estradiol, and progesterone in laying and nonlaying canvasback ducks (Aythya valisineria) ☆

Temporal changes in the levels of serum luteinizing hormone (LH), prolactin, estradiol, and progesterone associated with the reproductive patterns of 53 wild captive canvasback ducks were measured. The reproductive endocrinology of both laying and nonlaying females was compared in this 3-year study. Females that remained sexually inactive had ovaries with small, undeveloped follicles. Nonlaying ducks also had lower serum levels of LH (P less than 0.01), prolactin (P less than 0.05), estradiol, and progesterone than those of laying ducks in mid-April (during prelay), mid-May (on the fourth day of egg production), and mid-June (during postlay and incubation). Prolactin levels of both layers and nonlayers increased over this time interval (P less than 0.01) but levels of nonlayers were significantly lower than those of layers for the three blood-sampling dates. The low prolactin levels demonstrate that reproductive failure was not a result of inhibition by high serum prolactin levels. Intravenous injections of luteinizing hormone-releasing hormone (LHRH) in female canvasbacks resulted in significantly elevated (P less than 0.01) serum LH on the prelay blood sampling date. Lack of reproduction in nonbreeding canvasbacks was thus associated with low circulating serum LH levels but with LHRH-sensitive pituitary pools. These data suggest that lack of reproduction was a result of the failure of the hypothalamus to release releasing factors. The serum hormones of laying canvasbacks varied temporally with stages of the nesting cycle. LH levels increased prior to egg laying and fluctuated during the laying period. LH levels decreased at the onset of incubation but increased after loss of clutch, with renesting activity. Serum prolactin levels of layers were low prior to egg laying and increased gradually through laying of the first clutch, the renesting period, and laying of the second clutch. The highest prolactin levels occurred in ducks incubating their eggs. Prolactin levels decreased in ducks that failed to incubate their eggs. Serum estradiol levels increased sharply between 2 and 5 weeks prior to egg laying and remained high until the second day of egg production. Estradiol levels decreased when the fourth egg was produced, and remained low through the laying of the first clutch, the renesting period, and laying of the second clutch. Progesterone fluctuated widely through the nesting cycle, showing several major peaks before laying and another during incubation.

SERUM PROLACTIN LEVELS OF TURKEY HENS IN RELATION TO REPRODUCTIVE FUNCTION

Publisher Summary This chapter discusses the serum prolactin levels of turkey hens in relation to reproductive function. Serum prolactin levels of somatically mature, sexually immature photosensitive female turkeys, housed in a 6L: 18D photoperiod are low. In different experiments with birds of varying history mean levels of prolactin have varied from less than 5 ng/ml to as high as 20 ng/ml. The data were obtained from 8 large white strain turkeys. The hens had been held on a 6L:18D photoperiod and were changed to 15L: 9D on the first day of the experiment. Blood was drawn from the birds at 1300–1400 h each day. It appears from the data that the drop in feed consumption follows the behavioral manifestation of broodiness. The time course of changes in feed consumption and serum prolactin suggest that the drop in feed consumption is not a casual factor in increasing the serum prolactin. The composite data suggest that the prolactin levels increase before the increase in nesting. Most birds sampled follow this general pattern, however, one did not. This individual bird showed the behavioral manifestations of broodiness, the concomitant drop in feed consumption, and cessation of egg production but her serum prolactin level did not increase until after the onset of broodiness.

Involvement of catecholaminergic mechanisms in the photoperiodically induced rise in serum luteinizing hormone of Japanese quail (Coturnix coturnix japonica)

Abstract The involvement of brain catecholamines (CAs) in the neuroendocrine mechanisms that control the release of LH has been studied in somatically mature quail with regressed and with recrudescing testes and in sexually mature quail. In quail with recrudescing testes, serum LH was markedly increased 3 days after the onset of photostimulation. Administration of an inhibitor of CA synthesis, α-methyltyrosine (MT), started on the day of photostimulation and continued for 3 days thereafter, decreased brain dopamine (DA), norepinephrine (NE), and epinephrine (E) content and blocked the photoperiodically induced rise in serum LH. Treatment with bis(4-methyl-1-homopiperazinil-thiocarbonil) disulfide (FLA63), an inhibitor of DA-β-hydroxylase, caused a marked reduction of brain NE and E levels and a significant increase in brain DA content, and like MT, blocked the photoperiodically induced rise in serum LH. In sexually mature quail, serum LH and testicular regression were effected differently by MT and FLA63. MT partially reduced LH levels, but FLA63 suppressed them completely (i.e., to those of nonphotostimulated birds). Testicular weights were reduced by both MT and FLA63, but as with LH, the FLA63 was more effectual than MT. Treatment with l -dihydroxyphenylalanine, a direct precursor of DA, augmented DA content in the brain, caused a reduction of LH levels, and induced gonadal regression. The results are consistent with the hypothesis that NE-containing neurons facilitate central mechanisms which release LH in response to neural inputs involved in the photoperiodic stimulus, and that activation of DA-containing neurons is capable of inhibiting this release and inducing testicular regression.

A radioimmunoassay for turkey luteinizing hormone

Abstract A radioimmunoassay for the measurement of turkey LH (TLH) is described. The antiserum used was developed against purified TLH (No. 70355). Another TLH (CG-C) preparation was used for iodination and as a reference standard. Linear logit vs log dose plots were obtained with standard between 0.10 and 16.0 ng TLH/assay tube. Sera from laying famales, nonlaying females, intact males, castrate males, thyroidectomized males and broody females inhibit bindings of 125 I-TLH, yielding dose-response curves parallel to the standard curve. Sera from a hypophysectomized turkey, at levels up to 200 μl/assay tube did not inhibit binding of 125 I-TLH. Assay of TLH, added to hypophysectomized sera, resulted in essentially 100% recovery. Luteinzing hormone releasing hormone elicited an increase in immuroreactive LH within 10 min after injection. Castration of male turkeys resulted in elevated immunoreactive LH. Manipulation of the pituitary-thyroid axis yielded conflicting results. Thyroidectomy, triiodothyronine (T 3 ) and thyroxine (T 4 ) treatment, and thiouracil feeding had no effect on serum LH, but TRH injection elevated the immunoreactive material. Evidence is presented that suggests TRH releases LH in Aves .

Serum estradiol and progesterone levels of the laying turkey hen following acute treatment with mammalian luteinizing hormone or follicle-stimulating hormone ☆

Experiments were conducted to determine if a single intravenous injection of luteinizing hormone (LH) or follicle-stimulating hormone (FSH) would elicit an increase in serum progesterone (P) or estradiol (E) in the laying turkey. In all experiments, hens were used at 4–5 hr after oviposition when endogenous E and P were expected to be low. All E and P determinations were done by RIA. In Expt 1, hens were bled, then injected with 100, 250, 500 or 1000 μg of NIH-LH-B9 and bled again 5 and 30 min later. Increases in P were found with 100 and 500 μg of LH (P < 0.05) and 250 and 1000 μg LH (P < 0.01). E was increased by 250 (P < 0.01) and 1000 μg LH (P < 0.05). In Expt II, hens were bled, then injected with 250, 500, 750, or 1000 μg FSH-P (Armour-Baldwin Laboratories) and bled again 5 and 30 min later. P was increased by 500, 750, and 1000 μg of FSH (P < 0.01), while E levels were elevated by 250, 500, and 1000 μg FSH (P < 0.05). Therefore, the administration of either LH or FSH has a steroidogenic action on the turkey ovary eliciting rapid increases in serum P and E.

Release of gonadotropin-releasing hormone from the Japanese quail hypothalamus in vitro

The regulation of GnRH (gonadotropin-releasing hormone) secretion in Japanese quail was studied by maintaining excised hypothalamic slices containing the median eminence region in a continuous flow superfusion system. GnRH released into the superfusate was measured by radioimmunoassay using an antibody generated against synthetic GnRH. GnRH secretion increased in a dose-response manner when hypothalamic slices from female quail were exposed to superfusion medium containing elevated potassium ion concentrations. The potassium-induced GnRH release was found to be calcium dependent. GnRH was also increased when either 1 X 10(-6) M norepinephrine, epinephrine, or 1 X 10(-5) M of the beta-adrenergic agonist, isoproterenol was added to the superfusion medium. GnRH secretion from hypothalami of castrate and intact male quail was measured on Days 1, 10, and 21 of photostimulation and was elevated on Day 21. No differences were observed between the castrate and intact groups. It is concluded that GnRH is released from the quail hypothalamus in a manner analogous to mammals and that is release is subject to adrenergic stimulation.