Effects of centrifugation stress on pituitary-gonadal function in male rats

Abstract

The effects of centrifugation for various lengths of time were investigated on circulating levels of luteinizing hormone (LH) and testosterone in male rats. In a chronic 52-day experiment, centrifugation at 4.1 G significantly reduced LH and testosterone levels for the entire period. Centrifugation at 2.3 G had less effect inasmuch as LH levels were not significantly decreased and testosterone levels were significantly reduced only during the first few days of centrifugation. In more acute experiments, centrifugation at 4.1 G for 4 h resulted in reduced testosterone levels, whereas centrifugation for 15 min did not significantly alter the hormone levels. These results indicate that centrifugation can decrease circulating LH and testosterone levels if the gravitational force is of sufficient magnitude and is maintained for a period of hours. Chronic centrifugation may also inhibit the acute excitatory response of LH to handling and ether stress.

Urinary Excretion of LH and Testosterone from Male Rats During Exposure to Increased Gravity: Post‐Spaceflight and Centrifugation

“…Blood sampling at various time points during the periodic changes in plasma concentrations may mask the actual effects of microgravity and centrifugation. For example, in rats, plasma T was reduced over the first 4 days of centrifugation at 2.3 g (3); however, we have shown that excreted T was elevated over the first 8 days of centrifugation at 2 g (8). The use of 24‐hr urine excretion values is not biased by daily periodicity and may therefore provide a more accurate account of the effects induced by altered gravity on the pituitary‐gonadal axis.…”

“…Upon return to Earth, plasma LH was reported to be reduced on postspaceflight Day 8, whereas plasma T was elevated (4). During centrifugation at 2.3 g , plasma LH in rats was not significantly reduced, although plasma T was reduced on Days 1 and 4 with concentrations returning to control levels on Day 15 of exposure (3). Data from these studies suggest that a dissociation between plasma LH and T during exposure to altered gravity may exist.…”

“…In the present study, changes in LH and T were correlated during exposure to increased gravity induced postspaceflight or by centrifugation. However, previous studies of the effects of altered gravity on the pituitary‐gonadal axis have reported a dissociation between LH and T (3–5).…”

“…Rats centrifuged at 2.3 g exhibited reduced plasma T and unchanged plasma LH measured on the fourth day (3). Gray et al .…”

“…Testosterone (T) secretion in mammals is normally mediated by the gonadotropin, luteinizing hormone (LH). Exposure to altered gravity (i.e., microgravity and centrifugation) has been shown to affect the pituitary‐gonadal axis in mammals (1–4). During spaceflight, astronauts exhibited a significant increase in plasma LH; however, plasma T was reduced (4, 5).…”