Male Rats Secrete Luteinizing Hormone and Testosterone Episodically*

Abstract

We studied the temporal aspects of endocrine signaling between the pituitary gland and testes by measuring moment to moment changes in blood LH and testosterone levels in individual male rats. Each rat was fitted with an indwelling vascular cannula, and blood was withdrawn every 5 min for 8-12 h. Rats were maintained throughout the intensive blood-sampling period with an isotonic blood replacement mixture containing rat red blood cells and a human plasma protein preparation. LH and testosterone measurements were made in plasma volumes of 50 and 60 microliters. Most rats released LH in well defined pulses, characterized by a rapid increase in plasma LH within 5-10 min and a gradual decline lasting for the next 50-70 min. LH pulses occurred singly or in trains of two to four. Episodes of testosterone secretion spanned 3-6 h and were marked by a slowly graded rise and fall of plasma testosterone. In several instances, testosterone episodes were preceded (1-2 h) by a train of closely coupled LH pulses. Within a particular animal on different days, hormone episodes varied in number, amplitude, and timing. A particular hormone profile did not serve as a reliable hormone signature for an individual rat. Many rats displayed a characteristic sequence of 1) multiple LH pulses, 2) a sustained testosterone episode, and 3) a period of no LH pulses. This tripartite sequence of events is viewed as the essence of pituitary-testicular stimulation, and testicular negative feedback. Intermittent, short term fluctuations in peripheral levels of LH and testosterone represent the blood-borne, gland to gland signals controlling hypothalamic-pituitary-testicular function in the normal rat.

Testicular toxicity of profenofos in matured male rats

“…Firstly, increase in serum testosterone concentrations may be explained by the fact that the treatment causes an increase in serum LH concentrations in male rats, circulating LH is responsible for maintaining normal increased serum testosterone concentrations (Ellis and Desjardins, 1982 , 1980). The second speculation is virtually consistent with the present study of histopathologicaly, which included testicular destruction and degeneration represented by a single layer of tall columner epithelium, oedematous changes surrounding the seminiferous tubules, the cytoplasm of spermatogonia vaculated and these vacules contain dense and coallesed materials from degeneration and destruction of other organells, intracytoplasmic inclusion bodies in spermatogonia and abnormalities in spermatids besides elongation in Leydig cells.…”

Effects of Glucose on Thyrotrophin‐Releasing Hormone, Growth Hormone‐Releasing Hormone, Somatostatin and Luteinizing Hormone‐Releasing Hormone Release from Rat Hypothalamus in vitro

“…The RIA procedure for LHRH was similar to that previously reported (17). The LHRH antiserum (18) was kindly supplied by Dr Hamish Frazer, MRC Reproductive Biology Unit, Edinburgh, Scotland. The assay was incubated for 24 h at 4 "C without preincubation and then bound hormone was separated from free using dextran-coated charcoal.…”

Reflexive testosterone release: A model system for studying the nongenomic effects of testosterone upon male behavior

“…Coquelin and Desjardins [4] estimate that a young sexually mature male mouse will usually show around 6 or 8 spontaneous LH pulses per day or a pulse approximately every 3 to 4 hrs. If data from rats [5] are representative, these cycles likely proceed with similar regularity both during wakefulness and sleep.…”