Ageing does not influence the ultrashort feedback control of GnRH secretion in vitro.

Evidence indicates that long and short feedback systems are altered in the aged male rat. Data also indicate the existence of an ultrashort feedback mechanism controlling GnRH secretion. The present experiments were performed to test whether the ultrashort feedback control of GnRH is operating also in old male rats. Mediobasal hypothalami of 18-month-old male rats were perifused in vitro either in the presence or in the absence of a GnRH agonistic analogue (Buserelin: [D-Ser(TBU)6,Des-Gly10]GnRH ethylamide) and stimulated with 5-min pulses of K+ (for a total of six pulses) in order to test their ability to release GnRH. The hypothalamic fragment was exposed to the GnRH analogue either for a part of the experimental period (at the beginning or at the end) or for the whole duration of the perifusion. In both cases, the presence of the analogue diminished or totally abolished the responses to K+ stimulation. This is in line with the results obtained in young animals. The data suggest that the ultrashort feedback mechanism controlling GnRH release is normally functioning also in aged male rats despite the fact that other types of feedback mechanisms (long and short loop) are substantially altered.

[1]  P. Conn,et al.  Distribution of gonadrotropin releasing hormone agonist binding sites in the rat central nervous system , 1988, Brain Research.

[2]  F. Piva,et al.  Effects of aging on pituitary and testicular luteinizing hormone-releasing hormone receptors in the rat. , 1988, Life sciences.

[3]  M. Valença,et al.  Evidence for a negative ultrashort loop feedback mechanism operating on the luteinizing hormone-releasing hormone neuronal system. , 1987, Endocrinology.

[4]  M. Motta,et al.  Ultrashort feedback control of luteinizing hormone-releasing hormone secretion in vitro. , 1987, Endocrinology.

[5]  A. Carrillo,et al.  In vivo and in vitro examination of an autoregulatory mechanism for luteinizing hormone-releasing hormone. , 1987, Endocrinology.

[6]  L. Martini,et al.  In vitro release of luteinizing hormone-releasing hormone from the hypothalamus of old male rats. , 1987, Endocrinology.

[7]  D. Sirinathsinghji.  Regulation of lordosis behaviour in the female rat by corticotropin-releasing factor, β-endorphin/corticotropin and luteinizing hormone-releasing hormone neuronal systems in the medial preoptic area , 1986, Brain Research.

[8]  L. Frohman,et al.  Growth hormone (GH)-releasing factor stimulates hypothalamic somatostatin release: an inhibitory feedback effect on GH secretion. , 1986, Endocrinology.

[9]  M. Phillips,et al.  A biphasic excitatory response of hippocampal neurons to gonadotropin-releasing hormone. , 1986, Neuroendocrinology.

[10]  R. L. Moss,et al.  Hormonal modulation of the responsiveness of midbrain central gray neurons to LH-RH. , 1985, Neuroendocrinology.

[11]  K. Kendrick,et al.  Luteinizing hormone releasing hormone enhances proceptivity in a primate. , 1985, Neuroendocrinology.

[12]  R. Steiner,et al.  Reduced pulsatile luteinizing hormone and testosterone secretion with aging in the male rat. , 1984, Biology of reproduction.

[13]  K. Fuxe,et al.  Luteinizing hormone-releasing hormone increases dopamine turnover in the lateral palisade zone of the median eminence and reduces noradrenaline turnover in the nuc. Preopticus medialis of the hypophysectomized male rat , 1984, Neuroscience Letters.

[14]  D. Sarkar,et al.  Failure of prolactin short loop feedback mechanism to operate in old as compared to young female rats. , 1983, Endocrinology.

[15]  R. Steiner,et al.  Diminished luteinizing hormone pulse frequency and amplitude with aging in the male rat. , 1983, Endocrinology.

[16]  A. Negro-Vilar.  The median eminence as a model to study presynaptic regulation of neural peptide release , 1982, Peptides.

[17]  G. Hoffman,et al.  Age-related changes in dopamine, LHRH and somatostatin in the rat hypothalamus , 1980, Neurobiology of Aging.

[18]  M. A. Kowatch,et al.  Age-related alterations of isolated rat leydig cell function: gonadotropin receptors, adenosine 3',5'-monophosphate response, and testosterone secretion. , 1979, Endocrinology.

[19]  R. Walker,et al.  Age-related changes in reproductive hormones and in Leydig cell responsivity in the male Fischer 344 rat. , 1979, Journal of gerontology.

[20]  K. Pirke,et al.  A quantitative study on feedback control of LH by testosterone in young adult and old male rats. , 1978, Acta endocrinologica.

[21]  G. Riegle,et al.  Hypothalamic LH-releasing activity in young and aged intact and gonadectomized rats. , 1978, Experimental aging research.

[22]  G. Riegle,et al.  Serum LH Levels Following Multiple LHRH Injections in Aging Rats 1 2 , 1978, Proceedings of the Society for Experimental Biology and Medicine. Society for Experimental Biology and Medicine.

[23]  S. W. Chan,et al.  Testicular metabolism and serum testosterone in aging male rats. , 1977, Endocrinology.

[24]  J. Meites,et al.  Effect of aging on hypothalamic LH-releasing and prolactin inhibiting activities and pituitary responsiveness to LHRH in the male laboratory rat. , 1977, Journal of gerontology.

[25]  J. Meites,et al.  Effects of castration and gonadal steroids on serum luteinizing hormone and prolactin in old and young rats. , 1975, The Journal of endocrinology.