The effects of chronic exercise on metabolic and reproductive functions in male rats.

Previous studies concerning the effects of swimming on various endocrine gland functions have been performed. Our study was thus designed to analyze the effects of chronic exercise (swimming) on the resting metabolic rates (RMR) of adult rats. Most of the protocols used a water temperature of 33 C. It is our contention that such a protocol is not exclusively an exercise stress, but also a hypothermic stress. The protocol of our study was designed in a way that hypothermic stress was not part of the exercise stress. Male rats were swam in 36 C water for 3 hours a day, 5 days a week for 4 months. RMR of the animals were determined 24 h after the next to last swim session. Plasma hormone levels and epididymal sperm concentrations were determined in animals sacrificed 24 h after the last swim period. Exercising animals had a RMR 16% greater than that of control animals (p < 0.02), yet total and free thyroxine and total and free triiodothyronine were not significantly elevated. Neither plasma testosterone nor epididymal sperm counts were significantly reduced in the exercising animals. It appears that chronic exercise produces an elevation in RMR which is unrelated to thyroid gland activity and does not suppress the hypothalamic-pituitary-gonadal axis.

Adenylyl cyclase of perifused porcine granulosa cells remains responsive to pulsatile, but not continuous stimulation with follicle-stimulating hormone.

Differentiation of granulosa cells and development of ovarian follicles requires FSH for several days. The purpose of the present studies was to determine how the capacity of the adenylyl cyclase of immature porcine granulosa cells to respond to FSH depends on the dose, duration, and frequency of exposure to FSH. Cells were stimulated with various regimens of FSH and forskolin in a dynamic flow perifusion system. cAMP production during 4 h of continuous (tonic) exposure to FSH was directly related to FSH concentration (5-500 ng/ml). FSH-stimulated cAMP production declined markedly after 4 h of tonic stimulation with FSH, regardless of the FSH concentration. Preliminary experiments using a pulse interval of 3 h (perifusion medium FSH concentration, 150 ng/ml) indicated that stimulation with 15-min pulses elicited a greater cumulative cAMP response than stimulation with either 5-, 30-, or 60-min pulses. Responsiveness to FSH depended critically on the duration and frequency of stimulation and the concentration of FSH. Short pulses were more effective than long pulses in both eliciting cAMP responses of most uniform amplitude and maintaining responsiveness to a final tonic FSH stimulus. The optimal pattern of stimulation consisted of a pulse duration of 15 min, with a pulse interval of 2-3 h. A peak chamber FSH concentration of 150 ng/ml yielded the greatest cumulative cAMP production, although cells that had been perifused with FSH-free medium had the greatest response to a final tonic FSH stimulus. The attenuation of responsiveness after continuous perifusion with FSH does not appear to be due to desensitization of the cyclase itself, since 1) cells perifused with FSH continuously for 20 h still responded to forskolin (100 microM), which activates cyclase independently of the FSH receptor; and 2) cells did not become refractory to forskolin for 14 h. The transient refractoriness to FSH appears to be due to a process that alters the interaction between the FSH receptor and the guanine nucleotide regulatory component of cyclase. This refractoriness can be reversed simply by removing FSH from the perifusion medium for a critical period of time, i.e. 2-3 h.

The effect of dexamethasone on plasma glucose and liver glycogen levels in premetamorphic Rana catesbeiana tadpoles and frogs.

Premetamorphic Rana catesbeiana tadpoles and adult frogs demonstrate significant elevations in plasma glucose levels following dexamethasone (dex) injections. This response is greatest in the tadpole 24 hr after dex administration and is still detectable at 48 hr. Liver glycogen levels increase in the frog, but not in the tadpole, following daily injections of dex for five consecutive days. The response of the tadpole to dex occurs at a time when hepatic cytosolic glucocorticoid receptors have been observed, but when endogenous corticosterone is absent.

Binding of dexamethasone by hepatic, intestine, and tailfin cytosol in Rana catesbeiana tadpoles during spontaneous and triiodothyronine-induced metamorphosis.

The binding of the synthetic glucocorticoid dexamethasone (dex) to Rana catesbeiana tadpole liver, intestine, and tailfin cytosol during both spontaneous and triiodothyronine (T3)-induced metamorphosis has been examined. No change was observed in the dissociation constant (KD) in the liver or intestine during either spontaneous or T3-induced metamorphosis compared with liver and intestine cytosol from the frog. The binding capacity (N) in liver cytosol of premetamorphic tadpoles (14.33 x 10(-14) mol dex/mg protein) was not significantly different from that found during prometamorphosis (stage XVIII) (11.50 x 10(-14) mol dex/mg protein) and in the adult frog (19.24 x 10(-14) mol dex/mg protein). Following the onset of metamorphic climax, however, there were significant reductions in N in liver cytosol, reaching a nadir at stage XXIV (0.38 x 10(-14) mol dex/mg protein). Binding capacity in premetamorphic tadpole intestine (19.60 x 10(-14) mol dex/mg protein) was significantly reduced following premetamorphosis . Values did not return to premetamorphic values in the frog intestine (6.54 x 10(-14) mol dex/mg protein) as occurred in the frog liver, nor were values significantly reduced following the onset of metamorphic climax (10.43 x 10(-14) mol dex/mg protein) when compared with prometamorphosis (11.58 x 10(-14) mol dex/mg protein). The binding capacity in the tailfin cytosol did not deviate from premetamophic tadpole values (11.61 x 10(-14) mol dex/mg protein) through stage XXI (9.68 x 10(-14) mol dex/mg protein), the last stage in which sufficient tissue was available for analysis.