AJP - Endocrinology and Metabolism, Vol 265, Issue 2 E304-E313, Copyright © 1993 by American Physiological Society
LH pulsatility, biopotency, and clearance during undernutrition in orchidectomized mature rats
Q. Dong, B. Li, H. Rintala, S. Blair, J. Spaliviero and D. J. Handelsman
Department of Obstetrics and Gynecology, University of Sydney, New South Wales, Australia.
The effect of food restriction on circulating luteinizing hormone (LH)
levels in orchidectomized rats is controversial. The present study
demonstrates that decreasing food intake by 50% for 3-10 days in
orchidectomized rats increases LH pulse amplitude, length, area under pulse
curve, and mean levels but decreases LH pulse frequency compared with
ad-lib fed, orchidectomized controls. The effects on pulsatile LH secretion
of food reduction by 50% with or without dilution by cellulose to maintain
food volume in orchidectomized rats were also examined. Food volume
influences pulsatile LH secretion independent of macronutrient effect after
3 days of food restriction, but subsequently macronutrient deprivation
predominates. The exaggerated increase in LH levels in orchidectomized rats
subject to food restriction for 7 days was not due to immunochemical or
chromatographic heterogeneity or alteration in biopotency of circulating LH
molecules. Intravenously injected 125I-labeled rat LH analyzed by
noncompartmental modeling revealed that neither LH clearance nor mean
residence time was reduced by food restriction. We conclude that during
food restriction in orchidectomized rats, increases in LH pulse amplitude
exceed and precede the decreases in LH pulse frequency, although the early
changes in pulse amplitude are predominantly due to reduced food volume
rather than macronutrient deprivation.
