Determinants of the annual pattern of reproduction in mature male Merino and Suffolk sheep: responses to a nutritional stimulus in the breeding and non-breeding seasons

2003 ◽  
Vol 15 (1) ◽  
pp. 1 ◽  
Author(s):  
Maria J. Hötzel ◽  
Stephen W. Walkden-Brown ◽  
James S. Fisher ◽  
Graeme B. Martin
Keyword(s):  
Luteinizing Hormone ◽  
Breeding Season ◽  
Follicle Stimulating Hormone ◽  
Hormone Secretion ◽  
Pulse Frequency ◽  
Mature Male ◽  
Scrotal Circumference ◽  
Gonadotrophin Secretion ◽  
Gonadotrophin Releasing Hormone ◽  
Breeding Seasons

This study was designed to test whether an acute improvement in diet would increase gonadotrophin secretion and testicular growth in strongly photoperiod-responsive Suffolk rams and weakly photoperiod-responsive Merino rams in both the breeding (February–March) and the non-breeding (July–August) seasons. Mature rams (n = 5 or 6) of these breeds were fed a maintenance diet (0.9 kg chaff + 100 g lupin grain) or the same diet supplemented with 1.5 kg lupin grain for 42 days in each season. Lupin grain is a rich source of both energy and protein. Testosterone, luteinizing hormone (LH) and follicle stimulating hormone (FSH) were measured in plasma from blood sampled every 20 min for 24 h on Days −1, 12 and 35 relative to the change in feeding. In rams supplemented with lupins, body mass increased in both breeds in both seasons (P < 0.001). Scrotal circumference and LH pulse frequency increased with lupin supplementation in both seasons (P < 0.003) in Merinos, but only during the breeding season (P < 0.003) in Suffolks. Plasma FSH concentrations were affected by diet only during the breeding season, being elevated on Day 12 in lupin-supplemented rams of both breeds (P < 0.05). It was concluded that Merino rams exhibit reproductive responses to improved nutrition irrespective of time of the year, whereas Suffolk rams respond to nutrition only when the hypothalamic reproductive centres are not inhibited by photoperiod. Thus, Suffolks do respond to nutrition, just as Merinos do, but only when photoperiod allows. This difference between breeds appears to be a result of differences in the neuroendocrine pathways that control pulsatile gonadotrophin-releasing hormone secretion.

The effect of nutrition on testicular growth in mature Merino rams involves mechanisms that are independent of changes in GnRH pulse frequency

1995 ◽  
Vol 147 (1) ◽  
pp. 75-85 ◽  
Author(s):  
M J Hötzel ◽  
S W Walkden-Brown ◽  
M A Blackberry ◽  
G B Martin
Keyword(s):  
Body Weight ◽  
Breeding Season ◽  
Plasma Concentrations ◽  
Pulse Frequency ◽  
Testicular Growth ◽  
Scrotal Circumference ◽  
Gonadotrophin Secretion ◽  
Testicular Size ◽  
Pre Treatment ◽  
Short Term Experiment

Abstract In mature Merino rams, changes in diet to below or above the requirements for maintenance of body weight lead to changes in gonadotrophin secretion and testicular growth. However, the effects on testicular growth persist for much longer than those on LH and FSH secretion so that the gonadal and gonadotrophin responses are poorly correlated over time. This suggests that the gonadal effects may be partly independent of changes in the hypothalamic secretion of GnRH, an hypothesis tested in this study. In a short-term experiment (November, late spring, non-breeding season), we tested whether a high frequency of exogenous GnRH pulses could override the endogenous system and mimic the change in gonadotrophins seen in rams fed a high plane of nutrition. Mature Merino rams (scrotal circumference (mean ± s.e.m.) 33·6 ±0·5 cm, body weight (mean ± s.e.m.) 59·0 ± 0·9 kg) were fed 900 g chaff+1·6 kg lupin grain (High diet) or 360 g chaff+60 g lupin grain (Low diet) and infused with 8 pulses of GnRH or saline daily for 5 weeks (n=5/group). Blood was sampled every 20 min for 12 h on days – 1 and 14 relative to the start of treatments. Relative to pre-treatment levels, LH pulse frequency and FSH concentrations were decreased on day 14 in saline-infused rams fed the Low diet and increased in saline-infused rams fed the High diet (P<0·001). In GnRH-infused rams, gonadotrophin secretion was not affected by diet and the patterns of secretion of LH and FSH were similar to those in saline-infused rams fed the High diet. This model was used for a more complete endocrine analysis in a longer experiment designed to test the hypothesis that the effect of nutrition on testicular growth is partly independent of changes in the secretion of GnRH. The same treatments were imposed for 35 days on a different group of similar rams in March (autumn, mid-breeding season). Body weight and scrotal circumference were measured weekly and blood was sampled on days – 1 and 14. On days – 1 and 35, testosterone secretion in response to LH was tested by injecting exogenous ovine LH (NIADDK-oLH-25; 200 ng/kg body weight) to all rams. Body weight increased in rams fed the High diet and decreased in those fed the Low diet (P<0·001) and was not affected by infusion. The secretion of LH and FSH was affected by treatments as in experiment 1. There was an interaction between the effects of diet and infusion on change in scrotal circumference (P<0·02). In GnRH-infused rams fed the Low diet, scrotal circumference was not changed, so that from week 2 after the change in diet it was higher (P<0·05) than in saline-infused rams fed the Low diet and lower (P<0·05) than in both groups of rams fed the High diet. Changes in diet, GnRH pulse frequency or in testicular size did not affect mean plasma concentrations of inhibin or the testosterone response to LH. In conclusion, we have shown that in mature rams pulsatile exogenous GnRH cannot fully reproduce the effect that feeding a high diet has on testicular growth, suggesting that the effect of nutrition on testicular growth is partly independent of changes in the secretion of GnRH. Our results also show that (i) testicular growth induced by nutrition is not associated with changes in plasma concentrations of inhibin, or peripheral concentrations of testosterone after a pulse of LH, suggesting a dissociation of the endocrine and spermatogenic functions of the testis; (ii) changes in diet alter the secretion of gonadotrophins primarily by changing GnRH pulse frequency; and (iii) an exogenous GnRH pulsatile regimen can override endogenous secretion of a similar pulse frequency. Journal of Endocrinology (1995) 147, 75–85

EFFECT OF GONADECTOMY, SEASON AND THE PRESENCE OF FEMALE TAMMAR WALLABIES (MACROPUS EUGENII) ON CONCENTRATIONS OF TESTOSTERONE, LUTEINIZING HORMONE AND FOLLICLE-STIMULATING HORMONE IN THE PLASMA OF MALE TAMMAR WALLABIES

1980 ◽  
Vol 86 (1) ◽  
pp. 25-33 ◽  
Author(s):  
P. C. CATLING ◽  
R. L. SUTHERLAND
Keyword(s):  
Luteinizing Hormone ◽  
Breeding Season ◽  
Adult Male ◽  
Follicle Stimulating Hormone ◽  
Plasma Testosterone ◽  
Macropus Eugenii ◽  
Rapid Fall ◽  
Before And After ◽  
Breeding Seasons ◽  
Sexually Mature

Concentrations of FSH, LH and testosterone in plasma were measured in groups of adult male tammar wallabies before and after gonadectomy, and during the breeding and non-breeding seasons. Gonadectomy resulted in a rapid fall in plasma testosterone to undetectable levels by day 2, and significant increases in plasma LH and FSH levels. The concentrations of FSH, LH and testosterone did not change significantly between the non-breeding and breeding seasons in groups of male wallabies maintained in the absence of females. However, when male wallabies were associated with sexually mature females there were significant three- to fourfold increases in concentrations of LH and testosterone in plasma at the commencement of the breeding season. The observed increases in LH and testosterone were highly synchronized in the eight animals studied and occurred approximately 2 weeks before the synchronous onset of mating. Concentrations of FSH did not change significantly at this time.

Neurophysiological control of the secretion of gonadotrophin-releasing hormone and luteinizing hormone in the sheep--a review

1991 ◽  
Vol 3 (2) ◽  
pp. 137 ◽  
Author(s):  
JC Thiery ◽  
GB Martin
Keyword(s):  
Luteinizing Hormone ◽  
Steroid Receptors ◽  
Pulse Amplitude ◽  
Pulse Frequency ◽  
Neural Pathways ◽  
Releasing Hormone ◽  
Diagonal Band ◽  
Gonadotrophin Secretion ◽  
Gnrh Neurons ◽  
Gonadotrophin Releasing Hormone

The anterior pituitary gland secretes pulses of luteinizing hormone (LH) in response to pulses of gonadotrophin-releasing hormone (GnRH) released into the hypophysial portal blood by the hypothalamus. The pulsatile nature of the secretions is very important because the frequency of the pulses is directly related to the activity of the GnRH neurons. We can therefore take advantage of this phenomenon to develop mechanistic interpretations of responses to experimental treatments designed to unravel the neural pathways that influence what is, arguably, the most important individual signal controlling the activity of the reproductive system. We might also resolve the disagreements in the literature covering the neuropharmacology of gonadotrophin secretion. In this review, we describe work towards this end in the sheep. Most (95%) of the 2500 GnRH cell bodies in the sheep brain are located in a region covering the anterior hypothalamus, the medial preoptic area, the diagonal band of Broca, and the septum. The axons of up to 50% of these cells terminate in the organum vasculosum of the lamina terminalis. The remainder terminate in the median eminence and form the final common pathway for the many factors that affect gonadotrophin secretion. Among the factors known to affect the frequency of the pulses (or the activity of the GnRH neurons) are nutrition, pheromones, photoperiod and gonadal steroids (negative and positive feedback). Factors that affect GnRH pulse amplitude are more difficult to determine because variations in pituitary responsiveness prevent the use of LH patterns as a 'bioassay'. Techniques developed recently have allowed the direct measurement of GnRH pulse amplitude and revealed inhibitory effects of oestradiol, but we do not know whether this effect is due to a reduction in the amount of GnRH released by each neurone or a reduction in the number of neurones releasing a pulse. It is unlikely that the factors that alter pulse frequency do so by directly affecting the GnRH cells. For example, it is obvious that other cells, with specific receptors for pheromonal or nutritional stimuli, formulate a signal that is transferred to the GnRH cells via interneurones. Similarly, it is likely that a hypothalamic clock intervenes between photoperiodic inputs and GnRH output. Opioidergic neurons have been proposed as a link in this system, but the complexity of their action makes it unlikely that they directly affect the GnRH neurons. The responses to steroids are simple and rapid, but steroid receptors have not been found in GnRH cells, so at least one other set of interneurones is involved.(ABSTRACT TRUNCATED AT 400 WORDS)

Infertility

2013 ◽  
pp. 551-566
Author(s):  
John Reynard ◽  
Simon Brewster ◽  
Suzanne Biers
Keyword(s):  
Luteinizing Hormone ◽  
Male Infertility ◽  
Anterior Pituitary ◽  
Treatment Options ◽  
Follicle Stimulating Hormone ◽  
Reproductive Physiology ◽  
Seminiferous Tubules ◽  
Luteinizing Hormone Releasing Hormone ◽  
Releasing Hormone ◽  
Gonadotrophin Releasing Hormone

Male reproductive physiology 552 Aetiology and evaluation of male infertility 554 Investigation of male infertility 556 Oligozoospermia and azoospermia 560 Varicocele 562 Treatment options for male infertility 564 The hypothalamus secretes luteinizing hormone-releasing hormone (LHRH), also known as gonadotrophin-releasing hormone (GnRH). This causes the pulsatile release of anterior pituitary gonadotrophins called follicle-stimulating hormone (FSH) and luteinizing hormone (LH), which act on the testis. FSH stimulates the seminiferous tubules to secrete inhibin and produce sperm; LH acts on Leydig cells to produce testosterone (...

scholarly journals Neural Determinants of Pulsatile Luteinizing Hormone Secretion in Male Mice

Endocrinology ◽  
2020 ◽  
Vol 161 (2) ◽  
Author(s):  
Su Young Han ◽  
Isaiah Cheong ◽  
Tim McLennan ◽  
Allan E Herbison
Keyword(s):  
Luteinizing Hormone ◽  
High Frequency ◽  
Pulse Generator ◽  
Hormone Secretion ◽  
Pulse Frequency ◽  
Male Mice ◽  
Intact Male ◽  
Luteinizing Hormone Secretion ◽  
Pulse Profile ◽  
Lh Secretion

Abstract The gonadotrophin-releasing hormone (GnRH) pulse generator drives pulsatile luteinizing hormone (LH) secretion essential for fertility. However, the constraints within which the pulse generator operates to drive efficient LH pulsatility remain unclear. We used optogenetic activation of the arcuate nucleus kisspeptin neurons, recently identified as the GnRH pulse generator, to assess the efficiency of different pulse generator frequencies in driving pulsatile LH secretion in intact freely behaving male mice. Activating the pulse generator at 45-minute intervals generated LH pulses similar to those observed in intact male mice while 9-minute interval stimulation generated LH profiles indistinguishable from gonadectomized (GDX) male mice. However, more frequent activation of the pulse generator resulted in disordered LH secretion. Optogenetic experiments directly activating the distal projections of the GnRH neuron gave the exact same results, indicating the pituitary to be the locus of the high frequency decoding. To evaluate the state-dependent behavior of the pulse generator, the effects of high-frequency activation of the arcuate kisspeptin neurons were compared in GDX and intact mice. The same stimulus resulted in an overall inhibition of LH release in GDX mice but stimulation in intact males. These studies demonstrate that the GnRH pulse generator is the primary determinant of LH pulse profile and that a nonlinear relationship exists between pulse generator frequency and LH pulse frequency. This may underlie the ability of stimulatory inputs to the pulse generator to have opposite effects on LH secretion in intact and GDX animals.

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