Pituitary and gonadal response to exogenous LH-releasing hormone in the male domestic cat.
ABSTRACT To determine the influence of exogenous LH-releasing hormone (LHRH) on serum LH and testosterone, ten adult male domestic cats received three treatments on a rotating schedule at 10-day intervals as follows: (I) 0.1 ml saline i.m. (control); (II) 10 micrograms LHRH i.m., single injection; (III) 10 micrograms LHRH i.m., two injections given at a 2-h interval. Serial blood samples collected over a 360-min interval were analysed by radio-immunoassay for LH and testosterone. Although baseline serum LH values in saline-treated animals (treatment I) varied markedly among individual cats (2.2-29.2 micrograms/l), there was no evidence of pulsatile LH release or alterations in testosterone over time within individual males. In treatment II, the single injection of LHRH induced a rapid rise in mean serum LH within 30 min in all cats (mean peak, 88.2 +/- 9.8 micrograms/l), which returned to baseline by 120 min after LHRH. Mean testosterone increased within 30 min in this group (from 6.03 +/- 2.18 to 18.55 +/- 3.36 nmol/l), peaked at the 60-min collection (19.76 +/- 2.77 nmol/l) and returned to baseline by the 150-min sample. After treatment III, serum LH peaked at 131.6 +/- 13.6 micrograms/l within 30 min of the initial LHRH injection. A second injection of LHRH produced another LH surge within 30 min, but in all cats this second response was of a lower magnitude (mean peak, 69.0 +/- 14.5 micrograms/l) and shorter duration (P less than 0.05). The second LHRH injection sustained peripheral testosterone levels for approximately 1 additional h.(ABSTRACT TRUNCATED AT 250 WORDS)
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ABSTRACT: GnRH is the key neuropeptide controlling reproductive function in all vertebrate species. Two different neuroendocrine mechanisms have evolved among female mammals to regulate the mediobasal hypothalamic (MBH) release of GnRH leading to the preovulatory secretion of LH by the anterior pituitary gland. In females of spontaneously ovulating species, including rats, mice, guinea pigs, sheep, monkeys, and women, ovarian steroids secreted by maturing ovarian follicles induce a pulsatile pattern of GnRH release in the median eminence that, in turn, stimulates a preovulatory LH surge. In females of induced ovulating species, including rabbits, ferrets, cats, and camels, the preovulatory release of GnRH, and the resultant preovulatory LH surge, is induced by the receipt of genital somatosensory stimuli during mating. Induced ovulators generally do not show "spontaneous" steroid-induced LH surges during their reproductive cycles, suggesting that the positive feedback actions of steroid hormones on GnRH release are reduced or absent in these species. By contrast, mating-induced preovulatory surges occasionally occur in some spontaneously ovulating species. Most research in the field of GnRH neurobiology has been performed using spontaneous ovulators including rat, guinea pig, sheep, and rhesus monkey. This review summarizes the literature concerning the neuroendocrine mechanisms controlling GnRH biosynthesis and release in females of several induced ovulating species, and whenever possible it contrasts the results with those obtained for spontaneously ovulating species. It also considers the adaptive, evolutionary benefits and disadvantages of each type of ovulatory control mechanism. In females of induced ovulating species estradiol acts in the brain to induce aspects of proceptive and receptive sexual behavior. The primary mechanism involved in the preovulatory release of GnRH among induced ovulators involves the activation of midbrain and brainstem noradrenergic neurons in response to genital-somatosensory signals generated by receipt of an intromission from a male during mating. These noradrenergic neurons project to the MBH and, when activated, promote the release of GnRH from nerve terminals in the median eminence. In contrast to spontaneous ovulators, there is little evidence that endogenous opioid peptides normally inhibit MBH GnRH release among induced ovulators. Instead, the neural signals that induce a preovulatory LH surge in these species seem to be primarily excitatory. A complete understanding of the neuroendocrine control of ovulation will only be achieved in the future by comparative studies of several animal model systems in which mating-induced as well as spontaneous, hormonally stimulated activation of GnRH neurons drives the preovulatory LH surge.Frontiers in Neuroendocrinology 08/2000; 21(3):220-62. · 7.99 Impact Factor
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ABSTRACT: We investigated plasma luteinizing hormone (LH) concentration in domestic male cats challenged with Luteinizing Hormone Releasing Hormone Analog (LHRH-A) [des Gly 10, (DTrp6)-LHRH ethylamide] that mediates the function of the hypothalamic-pituitary-gonadal axis (HPG). Plasma LH concentrations in cats treated daily with LHRH (10 microg/100 microl/kg/day, subcutaneously-s.c.) for 19 days (LHRH group) and in controls treated with saline (NaCl-0.9%, same volume-SAL group) were chronically studied. LHRH administration (s.c.) for 15 days induced a significant fall (P < 0.05) in plasma LH concentrations during the chronic study. After the 15th day of treatment the groups were divided once more into animals treated with LHRH (10 microg/100 microl/kg) or saline (i.v.), and a time course study (300 min) was performed (acute study). Next, four groups of cats were compared in an acute study involving the s.c./i.v. administration of SAL/SAL, SAL/LHRH, LHRH/SAL, and LHRH/LHRH. The responses of the SAL animals challenged by acute i.v. administration of LHRH (group SAL/LHRH) were significantly higher (P < 0.01) than those of animals treated with LHRH (sc) (group LHRH/LHRH). LH release was also significantly increased in the latter group (P < 0.05), although the effect was short lasting, being recorded only at the first observation (45 min). An in vitro study with the pituitaries was also performed on day 20. Mean (+/-SEM) LH concentrations in the culture medium containing pituitaries with LHRH (10(-7) M) or saline were determined. In vitro analysis of these pituitaries demonstrated a significantly reduced response (P < 0.05) by animals treated sc with LHRH for 19 days. This study represents a source of data for the domestic cat going beyond its own physiology. Serving as a model, this animal provide important information for the study of reproductive physiology in other members of its family (Felidae), almost all of them threatened with extinction.Archives of Physiology and Biochemistry 07/2003; 111(3):254-8.
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ABSTRACT: This study describes 10 tomcats with different reproductive disorders. Two of the cats had abnormal sex chromosomes; one was a tortoiseshell and white Cornish rex, while the other was a brown Burmese. The other eight cats were diagnosed as having testicular hypoplasia, diphallos in combination with unilateral cryptorchidism, a persistent penile frenulum, retrograde ejaculation, temporary oligozoospermia, teratozoospermia, azoospermia and congenital poor libido. For the cat with a persistent penile frenulum, and the cat with a temporary oligozoospermia, the prognosis for successful reproduction was considered favourable. By contrast it was considered unlikely that the cats with chromosomal abnormalities, testicular hypoplasia, diphallos, retrograde ejaculation, teratozoospermia and azoospermia would be able to produce offspring.Journal of Small Animal Practice 09/1996; 37(8):394-401. · 1.18 Impact Factor