Influence of short-term fasting on the pituitary-testicular axis in normal men

To investigate whether short-term fasting affects serum testosterone (T) in normal subjects, 10 healthy men of normal weight were studied on two occasions: after an overnight fast (8 h), and after an additional 48 h of fasting. Blood glucose declined by 22 +/- 3% between the tests (p less than 0.001). Basal serum T fell from 8.7 +/- 0.7 to 5.7 +/- 0.8 micrograms/l (p less than 0.01), and LH from 6.9 +/- 0.8 to 5.0 +/- 0.7 U/l (p less than 0.01). Serum estradiol (E2) and FSH remained unaffected. To explore possible mechanisms behind the decreased basal release of T and LH, 9 small doses of glucose were given orally at regular intervals during a 56-hour fast to 9 additional normal men to maintain blood glucose levels. These men did not experience a fall in serum T or LH. Six additional normal men were given 50 micrograms GnRH intravenously after an overnight fast, and after a fasting period of 56 h. No acute increase in T was seen after the overnight fast, but after the 56-hour fast GnRH raised serum T by 55 +/- 14% (p less than 0.02). Moreover, fasting augmented the GnRH-induced LH response by 64 +/- 15% (p less than 0.02. These results imply that: short-term fasting exerts inhibitory influence on Leydig cell function via a mechanism which might involve a reduced hypothalamic and/or pituitary stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Increase of serum somatomedin C in hyperthyroid patients with pregnancy.

In thyrotoxic women with pregnancy, serum somatomedin C (SmC) concentration was markedly elevated (mean +/- SD 13.57 +/- 4.66 U/ml) compared to thyrotoxic women without pregnancy (1.24 +/- 1.09 U/ml), non-pregnant euthyroid women previously treated for hyperthyroidism (0.87 +/- 0.30 U/ml), normal subjects with pregnancy (6.08 +/- 3.36 U/ml) and pregnant euthyroid women previously treated for hyperthyroidism (5.98 +/- 1.52 U/ml). Since SmC/growth hormone ratio was significantly more in thyrotoxic pregnant women than in normal pregnant women and euthyroid pregnant women previously treated for hyperthyroidism, and since human placental lactogen (HPL), human chorionic gonadotropin (HCG) and prolactin (PRL) do not crossreact with SmC antibody, it is suggested that excess thyroid hormone during pregnancy results in excessive hepatic somatomedin C production.     

Relationship among thyrotropin (TSH), thyroid stimulating immunoglobulins, and results of triiodothyronine (T3) suppression test in patients with Graves' disease

To investigate the relationship between TSH and abnormal thyroid stimulator(s) in patients with hyperthyroid Graves' disease in whom normal thyroid hormone levels in the serum were maintained by antithyroid drug therapy and in patients with euthyroid Graves' disease, determinations were made of the TSH concentration, action of thyroid stimulating immunoglobulins (TSAb and TBII), and T3 suppression. Out of thirty-three patients with hyperthyroid Graves' disease, twelve patients with subnormal TSH levels were all non-suppressible according to the T3 suppression test results and the detectability of TSAb and/or TBII was as high as 75%. In three out of five patients with euthyroid Graves' disease, the serum TSH level was subnormal. All three showed non-suppressibility in the T3 suppression test and positive action of either TSAb or TBII. One of them became clinically thyrotoxic when the TSAb activity was further increased and TBII became positive, and was therefore diagnosed as having hyperthyroid Graves' disease. The present findings suggest that there are still abnormal thyroid stimulator(s) in patients with hyperthyroid Graves' disease who have low TSH, even if their thyroid hormone concentrations remain normal. Moreover, it is likely that some of the patients with euthyroid Graves' disease are actually in a state of subclinical hyperthyroidism because of the presence of abnormal thyroid stimulator(s).     

Androgen and progesterone effects on follicle-stimulating hormone and luteinizing hormone secretion in anestrous mares

Anestrous lighthorse mares were treated in December with dihydrotestosterone (DHT; 150 micrograms/kg of body weight), progesterone (P; 164 micrograms/kg), both DHT and P (DHT+P), testosterone (T; 150 micrograms/kg), or vehicle (n = 4/group). Daily blood sampling was started on Day 1, and on Day 4 all mares were administered a pretreatment injection of gonadotropin-releasing hormone (GnRH) and were bled frequently to characterize the responses of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) concentrations. Treatment injections were given on Day 4 and then daily through Day 17. On Day 18, all mares were again administered GnRH and were bled frequently. Treatment of mares with DHT, P, or T increased (p less than 0.01) plasma concentrations of these steroids to approximately 1.5 ng/ml during the last 10 days of treatment. There was no effect (p greater than 0.10) of treatment on LH or FSH concentrations in daily blood samples. Relative to the pretreatment GnRH injection, mares treated with T or DHT+P secreted approximately 65% more (p less than 0.01) FSH in response to the post-treatment GnRH injection; FSH response to the second GnRH injection was not altered (p greater than 0.10) in control mares or in DHT- or P-treated mares. There was no effect of any steroid treatment on LH secretion after administration of GnRH (p greater than 0.10). Averaged over all mares, approximately 94 times more FSH than LH was secreted in response to injection of GnRH.(ABSTRACT TRUNCATED AT 250 WORDS)     

Changes in the hypothalamic-hypophyseal axis of mares associated with seasonal reproductive recrudescence

Four groups of mares, representing anestrus (AN; n = 8), early transition (ET; n = 7), late transition (LT; n = 8) and estrus (EST; n = 12) were used to examine changes in the hypothalamus and anterior pituitary during the period of transition from winter anestrus into the breeding season. Mares were of mixed breeding, between the ages of 3 and 20 years, and had shown normal patterns of estrous behavior and ovulation during the breeding season previous to this experiment. Hypothalamic content of gonadotropin-releasing hormone (GnRH) and anterior pituitary content of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) were determined by radioimmunoassay. The number of receptors for GnRH in anterior pituitary tissue was also determined. There was no effect of stage of transition into the breeding season on receptors for GnRH or content of FSH (p greater than 0.05). Likewise, content of GnRH in the hypothalamus did not differ between the four groups (p greater than 0.05). However, pituitary content of LH increased progressively from anestrus to the breeding season (p less than 0.05). Means for the AN, ET, LT and EST groups were 1.1 +/- 0.2, 2.2 +/- 0.3, 6.3 +/- 1.4 and 15.2 +/- 1.8 micrograms LH/mg pituitary, respectively. In addition, serum concentrations of LH associated with the first ovulation of the year for 5 of the EST mares were significantly lower (p less than 0.01) than those associated with the second ovulation of the year.(ABSTRACT TRUNCATED AT 250 WORDS)     

Seasonal variation in hypothalamic content of gonadotropin-releasing hormone (GnRH), pituitary receptors for GnRH, and pituitary content of luteinizing hormone and follicle-stimulating hormone in the mare

Seasonal changes in the hypothalamic-hypophyseal axis were investigated using tissue from 49 light-horse mares, of mixed breeding. Hypothalamic and pituitary tissues were collected at 5 intervals throughout the years 1981 and 1982, representing midbreeding season (July, n = 10), transition out of the breeding season (October, n = 11), midanestrus (December, n = 8), transition into the breeding season (March, n = 10), and again in the following midbreeding season (July, n = 10). The hypothalamic region was dissected into preoptic area, body and median eminence. Gonadotropin-releasing hormone (GnRH) was extracted from hypothalamic samples with methanol-formic acid and quantified by radioimmunoassay. The anterior pituitary was homogenized and receptors for GnRH were quantified in a crude membrane fraction. Concentrations of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) were measured in the resulting supernatant. Content of GnRH in each of the 3 hypothalamic areas varied with season (P less than 0.01) and was lowest during midanestrus (P less than 0.05). There was no effect of season (P greater than 0.01) on either concentration or total number of receptors for GnRH, or concentration of FSH in the anterior pituitary. Concentrations of LH in the anterior pituitary varied with season (P less than 0.001). Means (+/- SEM) for the 5 collection times were 15.5 +/- 2.7, 9.7 +/- 2.4, 2.3 +/- 0.5, 2.7 +/- 0.4 and 11.7 +/- 1.5 microgram LH/mg anterior pituitary, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

Testosterone modulates the differential release of luteinizing hormone and follicle-stimulating hormone that occurs in response to changing gonadotropin-releasing hormone pulse frequency in the male monkey, Macaca fascicularis

Selective elevations of plasma follicle-stimulating hormone (FSH) levels are characteristic of some physiological conditions, such as the early stages of human puberty, and in some disorders of testicular function, such as idiopathic oligospermia. We tested the hypotheses that a slow gonadotropin-releasing hormone (GnRH) pulse frequency favors a selective elevation of plasma FSH and that this is influenced by the circulating steroidal milieu. We administered exogenous GnRH at frequencies of once every 90 min (q 90 min) and once every 240 min (q 240 min) to castrated prepubertal male monkeys who had received either empty (sham) or testosterone (T)-filled Silastic capsules at the time of castration. At the end of each experimental frequency period, mean plasma levels of luteinizing hormone (LH) and FSH were measured. Plasma T levels were also measured. Animals with T implants had plasma levels of this hormone that were in the adult range (approximately equal to 8 ng/ml), whereas those with sham implants had plasma T levels in the prepubertal range (less than or equal to 4 ng/ml). In animals with sham implants, mean plasma FSH levels were markedly elevated at the slower GnRH pulse frequency (39.5 +/- 3.6 ng/ml following GnRH q 240 min compared with 23.7 +/- 2.8 ng/ml following GnRH q 90 min). This selective FSH elevation was not apparent in animals with T implants. Mean plasma LH levels were similar (approximately equal to 8 micrograms/ml) at the two GnRH pulse frequencies, in both T-treated and sham-implanted animals.(ABSTRACT TRUNCATED AT 250 WORDS)     

Localization of biotinylated gonadotropin releasing hormone on pituitary monolayer cells with avidin-biotin-peroxidase complexes

The new avidin-biotin-peroxidase complex (ABC) technique was used to localize the [D-Lys6] analog of gonadotropin releasing hormone (GnRH), labeled with biotin, on pituitary monolayer cultures from female rats. Staining was diffuse, or in patches, on the surface of 10-17% of the cells 30 sec-3 min after the addition of 10(-10)-10(-12) M biotin-labeled GnRH. In parallel studies, double stains for gonadotropins showed label on 16.3 +/- 2% of the monolayers. Capping was evident by 3 min after exposure and the stain appeared in dense patches, vesicles, or granules 10-30 min after exposure. The stain was abolished by the addition of a 10- to 100-fold excess of unlabeled [D-Lys6] GnRH. Biotinylated GnRH released luteinizing hormone (LH) and follicle stimulating hormone (FSH) and was either equipotent or 10 times more potent than the unlabeled analog in multiple dose-response tests. The ED50 of the 4 hr release was 0.075 nM for LH and 0.02 nM for FSH. Competitive binding assays showed that the binding affinity of the biotinylated GnRH was within the range found for the unlabeled analog (0.7 nM-IC50). This report describes the localization of biotinylated GnRH on the surfaces of cells exposed to low concentrations of the analog with a technique that requires minimal manipulation of the cells, and is performed in less than one day.     

Reconciliation of the paradox that testosterone replacement prevents the postcastration hypersecretion of follicle-stimulating hormone in male rhesus monkeys (Macaca mulatta) with an intact central nervous system but not in hypothalamic-lesioned, gonadotropin-releasing hormone-replaced animals

Testosterone (T) replacement suppresses the postcastraction hypersection of follicle-stimulating hormone (FSH) in monkeys with an intact central nervous system (CNS), but not in hypothalamic-lesioned animals in which the pituitary-testicular axis is driven by an i.v. infusion of gonadotropin-releasing hormone (GnRH). One possible explanation for this finding is that T replacement markedly reduces the frequency of pulsatile GnRH release in CNS-intact animals. Under such a state of compromised hypophysiotropic drive to the gonadotropes, removal of a specific FSH-inhibiting factor would not be expected to lead to a hypersecretion of FSH. To test this hypothesis indirectly, adult monkeys were orchidectomized and immediately implanted with T-containing Silastic capsules to maintain circulating T concentrations in the upper physiological range, thereby preventing the postcastration hypersecretion of luteinizing hormone (LH) and FSH. An intermittent i.v. infusion of GnRH, identical to that used in studies with the hypothalamic-lesioned, GnRH-replaced model (1 microgram/min for 3 min every 3 h), was initiated 1 wk after castration and T replacement; subsequently, plasma LH and FSH concentrations were determined on Days 8 and 16-18 of GnRH treatment in samples collected every 20 min for 9 h. This GnRH stimulus resulted in a striking elevation in FSH concentrations from 5.2 +/- 1.5 ng/ml (mean +/- SE) before GnRH treatment to 62.6 +/- 20.8 and 118.3 +/- 33.1 ng/ml on Days 8 and 16-18 of GnRH treatment, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

Gonadotropin, prolactin and thyrotropin pituitary secretion after exogenous dehydroepiandrosterone-sulfate administration in normal women.

The effect of exogenous dehydroepiandrosterone-sulfate (DHAS) on luteinizing hormone (LH), follicle-stimulating hormone (FSH), prolactin (PRL) and thyroid-stimulating hormone (TSH) pituitary secretion was studied in 8 normal women during the early follicular phase. The plasma levels of these hormones were evaluated after gonadotropin-releasing hormone (GnRH)/thyrotropin-releasing hormone (TRH) stimulation performed after placebo or after 30 mg DHAS i.v. administration. The half-life of DHAS was also calculated on two subjects; two main components of decay were detected with half-times of 0.73-1.08 and 23.1-28.8 h. The results show an adequate response of all hormones to GnRH or TRH tests which was not significantly modified, in the case of LH, FSH and PRL, when performed in the presence of high levels of DHAS. However, the TSH response to TRH was significantly less suppressed (p less than 0.05) (39%) after DHAS administration than during repeated TRH stimulation without DHAS (51%). The data support the hypothesis that DHAS does not affect LH, FSH and PRL secretion, while TSH seemed to be partially influenced.     

Neonatal treatment of male rats with a gonadotropin-releasing hormone antagonist results in altered function of the pituitary-testicular axis in adult age

In most mammals, pituitary-testicular hormone secretion is very active during the perinatal period, but the physiological significance of this function for later pituitary-gonadal interactions and sexual maturation is largely unknown. Short-term neonatal treatment with gonadotropin-releasing hormone (GnRH) antagonist results in delayed sexual maturation and infertility in male rats. We have now extended our earlier findings and studied in more detail the pituitary-gonadal function in adult rats after such neonatal treatment. In this study, the pituitary-testicular activity of newborn male rats was temporarily blocked by treatment with a GnRH antagonist analogue (N-Ac-4-Cl-D-Phe1, 4-Cl-D-Phe2, D-Trp3, D-Phe6, des-Gly10-GnRH-D-alanylamide; Organon 30039; 2 mg/kg s.c. twice daily) on Days 1-5 of life. Timing of puberty was slightly delayed in the treated rats (average: 2 days, p less than 0.05), as determined by the age of the balano-preputial separation. In adult rats (90-110 days), only 3 of the 17 rats treated neonatally with GnRH antagonist were fertile (14 of 17 controls, p less than 0.01), despite normal circulating androgen levels. Pituitary and serum follicle-stimulating hormone (FSH) levels were slightly but consistently elevated (20-30%; p less than 0.05) in antagonist-treated animals, whereas luteinizing hormone (LH) levels (both immunoreactive and bioactive) were unaffected. The pituitary contents of GnRH receptors were increased in antagonist-treated animals 85 +/- 6.6 (mean +/- SEM, n = 19) vs. 58 +/- 4.1 fmol/gland in controls (n = 20; p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)     

Changes in plasma inhibin levels following pulsatile gonadotrophin-releasing hormone therapy in a man with idiopathic hypogonadotrophic hypogonadism

Changes in circulating inhibin levels were related to changes in testosterone (T) and the gonadotrophins luteinizing hormone (LH) and follicle-stimulating hormone (FSH) in a hypogonadotrophic hypogonadal man before and during pulsatile gonadotrophin-releasing hormone therapy which resulted in normal spermatogenesis. Before treatment, the plasma inhibin levels in the patient (210 +/- 50 U/l; mean +/- SD of four samples) were lower than in normal controls (552 +/- 150 U/l; p less than 0.01), as were T (1.1 nmol/l) and gonadotrophin (less than 1.0 IU/l) levels. Within 1 week of gonadotrophin-releasing hormone treatment, plasma LH (14.1 +/- 0.7 IU/l) and FSH (14.4 +/- 0.6 IU/l) reached supraphysiological levels. In response, T and inhibin concentrations increased progressively to reach high normal levels (27.7 +/- 1.6 nmol/l and 609 +/- 140 U/l) at 4 weeks, by which time the gonadotrophin levels stared to decline and gradually returned to the normal range between 12 and 24 weeks of treatment. There was a concomitant decrease in T and inhibin levels which remained within the normal range. The decline in the FSH level following the rise in testicular hormones was earlier and steeper than that of LH (37.5% decrease at 4 weeks vs. 30.4% at 12 weeks), suggesting that T and inhibin may act together to inhibit pituitary FSH secretion as opposed to LH secretion which is primarily controlled by T. It is concluded that, in man, during maturation of the pituitary-testicular axis, changes in circulating inhibin parallel those of T, and quantitatively normal inhibin secretion is dependent on gonadotrophin stimulation. FSH secretion may be regulated through negative feedback control, by both T and inhibin.     

Active immunization of intact mares against gonadotropin-releasing hormone: differential effects on secretion of luteinizing hormone and follicle-stimulating hormone

Five lighthorse mares were actively immunized against gonadotropin releasing hormone (GnRH) to determine the relative importance of this hypothalamic hormone in the secretion of luteinizing hormone (LH) and follicle-stimulating hormone (FSH). Five mares immunized against the conjugation protein served as controls. Mares were initially immunized in November and received secondary immunizations 4 wk later, and then at 6-wk intervals until ovariectomy in June. All mares immunized against GnRH exhibited an increase (p less than 0.01) in the binding of tritiated GnRH by plasma, an indication that antibodies against this hormone had been elicited. Concentrations of LH, FSH and progesterone in weekly blood samples were lower (p less than 0.05) in GnRH-immunized mares than in controls after approximately 4 mo of immunization. However, the LH concentrations were affected to a greater degree than were FSH concentrations. All five control mares exhibited normal cycles of estrus and diestrus in spring, whereas no GnRH-immunized mare exhibited cyclic displays of estrus up to ovariectomy. All mares were injected intravenously with a GnRH analog (which cross-reacted less than 0.1% with the anti-GnRH antibodies) in May, after all control mares had displayed normal estrous cycles, to characterize the response of LH and FSH in these mares; two days later, the mares were injected with GnRH. The LH response to the analog, which was assessed by net area under the curve, was lower (p less than 0.01) by approximately 99% in mares immunized against GnRH than in control mares. In contrast, the FSH response to the analog was similar for both groups.(ABSTRACT TRUNCATED AT 250 WORDS)     

Pituitary gonadotropins, hypothalamic gonadotropin-releasing hormone, and testicular traits of boars exposed to natural or supplemental lighting during pubertal development

Seventy crossbred boars were reared under natural (30 lux) or supplemental lighting (1000 lux) beginning at 4 wk of age. Boars received supplemental lighting from six 40-watt fluorescent bulbs between 0530 and 2030 h. Five boars from each treatment were killed at 67, 91, 119, 155, 182, 210, or 246 days of age. No differences (p greater than 0.05) in pituitary concentrations of luteinizing hormone (LH), follicle-stimulating hormone (FSH), and prolactin (PRL) were found between treatment groups at any age. Total pituitary content of LH, FSH and PRL increased as boars became older, but when expressed as hormone concentration, only PRL increased with age. Content of gonadotropin-releasing hormone (GnRH) in the pituitary stalk-median eminence, preoptic area, and hypothalamus proper was similar (p greater than 0.05) between treatments. When GnRH contents were totaled and combined for the treatment groups, it was found that GnRH content increased (p less than 0.05) as boars became older. No differences (p greater than 0.05) were observed in testicular volume percentage of seminiferous tubules and tubular diameter between lighting treatments. These data demonstrate that the supplemental lighting does not influence puberty in boars by altering hypothalamic content of GnRH or pituitary stores of LH, FSH, and PRL.     

Testosterone inhibits gonadotropin-releasing hormone pulse frequency in the male sheep

The objective was to determine the effect of chronic testosterone (T) treatment on GnRH and LH secretion in wethers. Rams were either castrated only or castrated and immediately treated with Silastic implants containing T. Several weeks later, a device for collecting hypophyseal-portal blood was surgically implanted. Six to seven days later, blood samples were collected simultaneously and continuously from the portal vessels and jugular vein of pairs of conscious animals. Samples were divided at 10-min intervals for 6-12 h. One hour before the end of collection, all animals received i.v. injections of 250 ng of GnRH. In samples collected simultaneously from 6 pairs of animals, T reduced the frequency of both GnRH pulses (1.8 +/- 0.2 vs. 0.9 +/- 0.3/h, p less than 0.03) and LH pulses (1.6 +/- 0.1 vs. 0.8 +/- 0.3/h, p less than 0.03). T did not alter amplitude of either GnRH or LH pulses. Testosterone reduced mean GnRH (9.7 +/- 0.6 vs. 7.9 +/- 0.5 pg/ml, p less than 0.05), whereas mean LH was not significantly reduced (9.6 +/- 1.4 vs. 6.1 +/- 1.8 ng/ml, p = 0.16). These results support the hypothesis that T reduces GnRH pulse frequency.     

Feedback effects of ovarian steroids on the hypothalamic-hypophyseal axis in the rabbit

The feedback effects of two ovarian steroids, estradiol-17 beta (E2) and 20 alpha-hydroxypregn-4-en-3-one (20 alpha OH), were examined in both intact (INT) and ovariectomized (OVEX) does. We measured steroid-induced alterations in endogenous gonadotropin-releasing hormone (GnRH) from sequential 10-min samples of hypothalamic perfusates, simultaneous changes in peripheral plasma luteinizing hormone (LH) and follicle-stimulating hormone (FSH), and the modification of pituitary responsiveness, i.e., increments in plasma LH (delta LH) and plasma FSH (delta FSH), after 50 ng, 250 ng, and 1 microgram of exogenous GnRH in individual does of 6 treatment groups. The groups were: INT does, OVEX does, OVEX does receiving either one (1 E2) or two (2 E2) E2-filled Silastic capsules, OVEX does receiving a 20 alpha OH-filled capsule (20 alpha OH), and OVEX does receiving both capsules of E2 and 20 alpha OH (1 E2 + 20 alpha OH). Ovariectomy enhanced the pulsatile release of hypothalamic GnRH and pituitary LH and FSH, and increased the LH response (delta LH) to exogenous GnRH (OVEX vs. INT, p less than 0.05). Replacement of E2 at the time of ovariectomy prevented the increased GnRH and gonadotropin secretion as well as the enhanced delta LH that were observed in untreated OVEX does. The release of hypothalamic GnRH in the 20 alpha OH group was lower (p less than 0.05) than that in the OVEX group and not different from that in the INT group. The release of pituitary LH and FSH and the delta LH in the 20 alpha OH group was not different from that in the OVEX group, but these parameters were greater (p less than 0.05) than those in the INT group. The hypothalamic GnRH pulse frequency in the 1 E2 + 20 alpha OH group was lower (p less than 0.05) than that in either the 1 E2 or the 20 alpha OH group, but the delta LH in the 1 E2 + 20 alpha OH group was not different from that in either the 1 E2 or the 20 alpha OH group. The highest dose (1 microgram) of exogenous GnRH stimulated a modest increase in FSH in the OVEX, 20 alpha OH, 1 E2 + 20 alpha OH, and 1 E2 groups; but a steroid effect on delta FSH among these 4 groups was not apparent.(ABSTRACT TRUNCATED AT 250 WORDS)     

Identification of the TRH-like peptides pGlu-Glu-Pro amide and pGlu-Phe-Pro amide in rat thyroid: regulation by thyroid status.

Rat thyroid contains thyrotropin-releasing hormone (TRH) and TRH-like peptides which react with TRH antisera. We have identified the TRH-like peptides in the thyroid and examined whether their levels are influenced by thyroid status. The peptides were extracted from the thyroid glands of five hyperthyroid rats and purified by ion-exchange chromatography on SP-Sephadex C25 and reversed-phase high performance liquid chromatography. The principal TRH-immunoreactive component exhibited the same retention on HPLC as synthetic pGlu-Glu-Pro amide and a secondary component corresponded to synthetic pGlu-Phe-Pro amide. In agreement with these assignments the main peptide was shown to be acidic when chromatographed on DEAE-Sephadex A25 and the second peptide neutral. The levels of TRH and TRH-like peptides in the thyroid were investigated in hyper-, hypo- and euthyroid rats. Hyperthyroidism was induced by chronic subcutaneous administration of triiodothyronine (T3) and hypothyroidism was produced by addition of propylthiouracil (PTU) to the drinking water. The amounts of the peptides were determined by radioimmunoassay with a TRH-antiserum, carried out after extraction from the tissues and purification by ion exchange chromatography. The mean concentration of TRH-like peptides in the thyroids of the hyperthyroid rats was 95.5+/-25.5 pmol/g, the mean concentration in the hypothyroid rats was 11.7+/-3.4 pmol/g, and in the euthyroid rats 17.6+/-3.2 pmol/g. The concentrations of TRH were less influenced by thyroid status: the values in hyper-, hypo- and euthyroid rats were 47.5+/-9.4, 42.1+/-6.3, and 17.2+/-1.6 pmol/g respectively. The results show that the levels of the TRH-like peptides in rat thyroid are highly sensitive to thyroid status, suggesting a possible involvement in thyroid regulation.     

Altered relationship between protonmotive force and respiration rate in non-phosphorylating liver mitochondria isolated from rats of different thyroid hormone status

We have determined the relationship between rate of respiration and protonmotive force in oligomycin-inhibited liver mitochondria isolated from euthyroid, hypothyroid and hyperthyroid rats. Respiration rate was titrated with the respiratory-chain inhibitor malonate. At any given respiration rate mitochondria isolated from hypothyroid rats had a protonmotive force greater than mitochondria isolated from euthyroid controls, and mitochondria isolated from hyperthyroid rats had a protonmotive force less than mitochondria isolated from euthyroid controls. In the absence of malonate mitochondrial respiration rate increased in the order hypothyroid less than euthyroid less than hyperthyroid, while protonmotive force increased in the order hyperthyroid less than euthyroid less than hypothyroid. These findings are consistent with a thyroid-hormone-induced increase in the proton conductance of the inner mitochondrial membrane or a decrease in the H+/O ratio of the respiratory chain at any given protonmotive force. Thus the altered proton conductance or H+/O ratio of mitochondria isolated from rats of different thyroid hormone status controls the respiration rate required to balance the backflow of protons across the inner mitochondrial membrane. We discuss the possible relevance of these findings to the control of state 3 and state 4 respiration by thyroid hormone.     

Progesterone does not affect the amount of mRNA for gonadotropins in the anterior pituitary gland of ovariectomized ewes

To evaluate the effect of progesterone on the synthesis and secretion of gonadotropins, ovariectomized ewes either were treated with progesterone (n = 5) for 3 wk or served as controls (n = 5) during the anestrous season. After treatment for 3 wk, blood samples were collected from progesterone-treated and ovariectomized ewes. After collection of blood samples, hypothalamic and hypophyseal tissues were collected from all ewes. Half of each pituitary was used to determine the content of luteinizing hormone (LH) and follicle-stimulating hormone (FSH), and the number of receptors for gonadotropin-releasing hormone (GnRH). The amounts of mRNA for LH beta subunit, FSH beta subunit, alpha subunit, growth hormone, and prolactin were measured in the other half of each pituitary. Treatment with progesterone reduced mean serum concentrations of LH (p less than 0.001) but ot FSH (p greater than 0.05). Further, progesterone decreased (p less than 0.05) the total number of pulses of LH. We were unable to detect pulsatile release of FSH. Hypothalamic content of GnRH, number of receptors for GnRH, pituitary content of gonadotropins and mRNA for LH beta subunit, FSH beta subunit, alpha subunit, growth hormone, and prolactin were not affected (p greater than 0.05) by treatment with progesterone. Thus, after treatment with progesterone, serum concentrations of LH (but not FSH) are decreased. This effect, however, is not due to a decrease in the steady-state amount of mRNA for LH beta or alpha subunits.     

Effects of season and testosterone treatment on gonadotrophin secretion and pituitary responsiveness to gonadotrophin-releasing hormone in castrated Romney and Poll Dorset rams.

In castrated rams (Romney and Poll Dorset, n = 8 for each breed), inhibition by testosterone treatment (administered via Silastic capsules) of luteinizing hormone (LH) pulse frequency, basal and mean LH concentrations, mean follicle-stimulating hormone (FSH) concentration, and the peak and total LH responses to exogenous gonadotrophin-releasing hormone (GnRH) were significantly (P less than 0.01) greater during the nonbreeding than during the breeding season. Poll Dorset rams were less sensitive to testosterone treatment than Romney rams. In rams not receiving testosterone treatment, LH pulse frequency was significantly (P less than 0.05) lower during the nonbreeding season than during the breeding season in the Romneys (15.8 +/- 0.9 versus 12.0 +/- 0.4 pulses in 8 h), but not in the Poll Dorsets (13.6 +/- 1.2 versus 12.8 +/- 0.8 pulses in 8 h). It is concluded that, in rams, season influences gonadotrophin secretion through a steroid-independent effect (directly on hypothalamic GnRH secretion) and a steroid-dependent effect (indirectly on the sensitivity of the hypothalamo-pituitary axis to the negative feedback of testosterone). The magnitude of these effects appears to be related to the seasonality of the breed.