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Restoration of Pulsatile Luteinizing Hormone Secretion after Fasting in Rhesus Monkeys (Macaca mulatta): Dependence on Size of the Refeed Meal^*

Departments of Behavioral Neuroscience University of Pittsburgh, Pittsburgh, Pennsylvania 15213
Departments of Behavioral Neuroscience, Psychiatry, and Physiology, University of Pittsburgh Pittsburgh, Pennsylvania 15213

Address all correspondence and requests for reprints to: Dr. Judy L. Cameron, Department of Psychiatry, University of Pittsburgh School of Medicine, 3811 O'Hara Street, Pittsburgh, Pennsylvania 15213.

Abstract

In men and adult male rhesus monkeys brief periods of fasting (i.e. 1–2 days) can often lead to a suppression of hypothalamic-pituitary-testicular axis activity, marked by decreased circulating concentrations of LH, FSH, and testosterone. Refeeding a normal meal can rapidly restore normal secretory patterns of LH and testosterone. To learn more about the nature of the signal that links reproductive hormone secretion to nutrient intake, we examined whether the degree of restoration of pulsatile LH and testosterone secretion after a brief period of fasting is influenced by the size of the refeed meal. Adult male rhesus monkeys had indwelling venous catheters surgically implanted and were maintained on swivel/tether systems for remote collection of blood samples. Monkeys were fasted for 1 day and then on the following day they were refed one of five meals which varied in size and calorie content (i.e. 0 Cal/0 pellets Purina monkey chow; 100 Cal/5 pellets; 200 Cal/10 pellets; 300 Cal/15 pellets; or 600 Cal/30 pellets). Blood samples were collected from 0800–2400 h at 20-min intervals on the days of refeeding and assayed for LH and testosterone content. After a day of fasting, the frequency of pulsatile LH secretion the following morning was very low (0.56 ± 0.1 pulses/3 h, measured from 0800–1100 h). When monkeys were not refed (i.e. were subjected to a second day of fasting; 0 pellet group) LH pulse frequency remained low [2.88 ± 0.72 pulses/13 h, measured from 1100–2400 h (equivalent to 0.66 pulses/3 h)] throughout the day and evening hours. Refeeding monkeys 5, 10, 15, and 30 pellets caused a progressive stimulation of pulsatile LH secretion (3.17 ± 0.54, 3.67 ± 0.56, 5.5 ± 0.67, and 6.38 ± 0.53 pulses/13 h, respectively). Like LH pulse frequency, mean circulating LH and testosterone concentrations progressively increased as the size of the refeed meal was increased. For all three parameters (i.e. LH pulse frequency, mean LH concentration, and mean testosterone concentration) there was a significant, P 0.001, linear trend with increasing meal size. These findings indicate a very strong relation between the level of nutritional intake and the level of central drive to the reproductive axis during nutritional recovery from fasting, and suggest a physiological parameter that responds in a progressive fashion to increasing food intake serves as the signal to link central drive to the reproductive axis to changes in nutrient intake. These results provide further evidence that relatively short term fluctuations in nutritional intake can play an important role in modulating the central drive to the reproductive axis in male primates.

Footnotes

^* These studies were supported by NIH Grants HD-20789, HD-26888, and HD-08610. Preliminary findings from the studies were presented at the 20th Annual Meeting of the Society for Neuroscience, St. Louis, 1990 (Abstract 168.18).

Received January 7, 1991.

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