Biomedical subjects
Publications and source records attributed to J P Preslock.
Ascorbic acid (AA) can transiently stimulate LH and FSH release from superfused male hamster anterior pituitary glands. The effective concentration is 1 mM or higher. Since 8-Br-cAMP or 8-Br-cGMP can not mimic the AA stimulation pattern, the action mechanism is not mediated through cyclic nucleotide system.
A continuous flow superfusion system which was previously developed in our laboratory was utilized to study the modulation of LH and FSH release by cyclic nucleotides and LHRH from anterior pituitary glands (APG) obtained from rats or hamsters. There was a transient increase in LH and FSH secretion from superfused rat APG in response to superfusion with 1 X 10(-3) M 1-methyl-3-isobutyl-xanthine (MIX), while 1 X 10(-4) MIX M had no effect. Furthermore, a dose of 5 X 10(-5) M MIX did not potentiate the gonadotrophin-releasing effect of 1 X 10(-10) M LHRH. Neither 1 X 10(-3) M 8-Br-cAMP nor 1 X 10(-3) M 8-Br-cGMP mimicked the gonadotrophin-releasing effects of 1 X 10(-9) M LHRH. In the experiments utilizing hamster APG, FSH release gradually increased during superfusion with 1 X 10(-3) M MIX or 1 X 10(-4) M MIX, while LH release was transient but significantly increased in response to superfusion with both doses of MIX. A dose of 5 X 10(-5) M MIX potentiated the effect of a low dose of LHRH (1 X 10(-10) M) upon both LH and FSH secretion. 1 X 10(-3) M 8-Br-cAMP mimicked the effect of LHRH upon LH and FSH released from superfused hamster APG, while 1 X 10(-3) M 8-Br-cGMP was inhibitory. These results suggest that cyclic nucleotides are involved in the mediation of the LHRH-induced release of gonadotropins from the anterior pituitary gland of the hamster, but do not mediate the LHRH-induced release of gonadotropins from the rat anterior pituitary gland.
Bilateral lesions were placed in the sexually dimorphic nucleus of the preoptic area (SDN-POA) in castrated adult male rats in an attempt to determine a physiologic role for this nucleus. These lesions significantly attenuated the increase in plasma FSH and LH due to simultaneous castration at 24 hr, and at 7 and 14 days following surgery, and significantly decreased the levels of plasma prolactin on comparison with pre-operative values and those of castrated controls. When rats were castrated and lesions placed at 14 days following castration, plasma levels of FSH, LH and prolactin were significantly decreased at 24 hr and at 7 days following surgery. Lesions which were placed lateral or caudal to the SDN-POA simulated the effects of lesions placed within the SDN-POA upon plasma LH, FSH and prolactin, with lateral lesions being most effective. However, lesions which were placed dorsal or rostral to the SDN-POA had no effect. The results of these studies suggest that the SDN-POA may be involved in the regulation of LH, FSH, and prolactin release.
Melatonin initially inhibited FSH secretion from superfused adult male hamster anterior pituitary glands obtained at 8:30 a.m. However, there was a gradual rebound during melatonin superfusion followed by an overshoot above baseline when melatonin was discontinued (morning response). Melatonin continuously inhibited FSH secretion during superfusion of hamster anterior pituitary glands obtained at 3:30 p.m., with a rebound evident only when melatonin was withdrawn (afternoon response). Melatonin continuously inhibited LH secretion from these superfused pituitaries, with a return to baseline levels only upon melatonin withdrawal. Prior pinealectomy or constant light could reverse the FSH morning response to an afternoon response, and late-morning melatonin injections could reverse the FSH afternoon response to a morning response. Neither prior pinealectomy, constant light nor melatonin injections affected melatonin inhibition of LH secretion from superfused pituitary glands. These results suggest that melatonin differentially inhibits FSH and LH secretion from isolated superfused hamster anterior pituitary glands.
The effect of chronic daily afternoon injections of melatonin upon basal and melatonin-modulated release of FSH and LH was investigated in superfused hamster anterior pituitary glands. The basal release rate of both FSH and LH began to decline following the beginning of melatonin injections, and reached a nadir after six weeks. Basal release rate of FSH and LH then began to spontaneously increase and reached a plateau at 13 weeks of injections. The inhibition by melatonin upon FSH and LH release in vitro gradually declined during the period of melatonin injections. After six weeks of melatonin injections the release rate of FSH was no longer suppressed by melatonin superfusion, while the release rate of LH became refractory to melatonin suppression in vitro after nine weeks of melatonin injections. These results demonstrate a change in the release rates of both basal and melatonin-inhibited gonadotropin release during melatonin-induced testicular regression and recrudescence in hamsters.
The purpose of these experiments was to determine whether bilateral vasoligation of adult male rats had any short-term effects upon plasma levels of follicle-stimulating hormone (FSH), luteinizing hormone (LH), and prolactin. Adult male rats (250-300 g) were either bilaterally vasoligated or sham vasoligated, and blood samples were obtained by cardiac puncture preoperatively and at 24 h and 7 days following surgery. Plasma levels of both FSH and LH were significantly (P less than 0.01) decreased at 24 h following vasoligation compared to preoperative levels and those of sham-operated controls. However, the response was differential since, at 7 days following vasoligation, plasma FSH was still significantly decreased while LH was returning to control levels. Conversely, plasma prolactin levels were significantly (P less than 0.01) increased at 24 h compared to preoperative values and those in sham-operated controls, and at 7 days prolactin had returned to preoperative control levels. Sham vasoligation did not significantly change plasma levels of FSH, LH, or prolactin at any of the time intervals investigated. These results provide further evidence that suggests that there may be a direct connection between the testis and central nervous system that may be involved in the short-term regulation of gonadotropin and prolactin secretion.
The adult male golden hamster will undergo testicular regression when exposed to a short photoperiod, blinding, or late afternoon injections of melatonin. The present study was conducted to compare the effects of all three treatments on serum gonadotropin levels and testicular weights, and to evaluate the effects of these treatments on hypothalamic content of both immunoreactive and bioactive luteinizing hormone-releasing hormone (LHRH) levels. Hamsters were blinded (BL), exposed to a short photoperiod (SP), or received daily injections of melatonin (MEL) for 15 wk. Each treatment (BL, SP, MEL) induced a temporally similar decline in serum luteinizing hormone (LH), serum follicle-stimulating hormone (FSH), and testicular weight. Spontaneous recrudescence occurred earliest in the MEL group, with serum gonadotropins and testicular weight returning to normal by 15 wk. The SP group exhibited recovery of serum gonadotropins but not testicular weight by 15 wk. The BL group demonstrated partial recovery of serum FSH levels by 15 wk, with no recovery in either serum LH or testicular weight. Each treatment group demonstrated increased hypothalamic content of immunoreactive LHRH which was temporally correlated with the decreases of serum gonadotropins. Additionally, the MEL and SP groups demonstrated decreased immunoreactive LHRH levels during spontaneous recrudescence. Extracts of hypothalami from all treatment groups were bioactive on control hamster pituitary cells. These results indicate that there are temporal differences among the three common treatments and that these differences are manifested in serum gonadotropins, testicular weight and hypothalamic LHRH. Hypothalamic LHRH levels determined by radioimmunoassay and bioassay show periods of increase and decrease which coincide with periods of altered serum gonadotropin levels in all groups.
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Procedures designed to express pineal-mediated antigonadotropic activity were performed upon male house mice. Neither blinding nor blinding plus olfactory bulbectomy of house mice resulted in testicular involution within 12 weeks. The pineal gland appears to be of little significance to reproduction in the house mouse.
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Studies were undertaken to investigate testicular steroidogenesis in the Rhesus monkey Macaca mulatta. Testicular fragments (50 mg) were incubated for 3 hr with pregnenolone-7-3H or with progesterone-7-3H. The major metabolite of pregnenolone was progesterone (70.1%), with a lesser conversion to 17-hydroxyprogesterone (1.6%), androstenedione (3.3%), and testosterone (7.2%). The delta-5 intermediates 17-hydroxypregnenolone (4.6%) and dehydroepiandrosterone (8.6%) were also identified in the pregnenolone incubates. A majority of the progesterone substrate was not metabolized by the testicular fragments (80.1%), while some conversion to 17-hydroxyprogesterone (3.4%), androstenedione (4.8%), and testosterone (11.7%) occurred in the incubates. These results suggest that testicular fragments from the Rhesus monkey may convert pregnenolone to testosterone through both the delta-4 and the delta-5 pathways.
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We recently reported that the baboon testis converts pregnenolone to testosterone through the delta-4 pathway. The present studies were to determine the metabolism of intermediates of the delta-4 and delta-5 pathway by the baboon testis. Fragments (50 mg) were incubated for 3 hr with 10 muCi of the following tritium-labelled substrates: pregnenolone, progesterone, 17-hydroxypregnenolone, 17-hydroxyprogesterone, dehydroepiandrosterone, androstenedione, or testosterone. Pregnenolone was converted to testosterone primarily through the delta-4 pathway, with accumulation of progesterone, 17-hydroxyprogesterone and 20alpha-dihydroprogesterone as predominant intermediates. Similar results were obtained in progesterone incubations. 17-hydroxyprogesterone was not efficiently metabolized by the fragments, while 17-hydroxypregnenolone and dehydroepiandrosterone were efficiently converted into testosterone and androstenedione. Androstenedione was metabolized primarily to testosterone, while testosterone was not a suitable substrate. Some 5alpha-androstanediol was identified in each incubate. These results suggest that although testosterone is formed from pregnenolone through the delta-4 pathway, the delta-5 intermediates are more suitable substrates for testosterone synthesis in the baboon testis.
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