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J. F. Hasler, A. E. Buhl and E. M. Banks

Summary.

The effect of photoperiod on sexual function and growth in weanling male and female collared lemmings (Dicrostonyx groenlandicus) was studied. Males and females maintained in 6 hr light:18 hr dark after weaning were larger at the end of 70 days than their siblings kept in 20L:4D. Males in 6L: 18D were longer and overall body growth was greater. Males in 6L:18D had heavier adrenals but there were no differences in the weights of testes, preputial glands or seminal vesicles or in the mean testosterone levels of the two groups. Females in 6L:18D had heavier preputial glands than the 20L:4D females. There were no differences between the two groups in uterine, ovarian or adrenal weights or in the number or mean size of atretic or healthy Graafian follicles. Adult males kept in 6L:18D increased more in body weight than those in 20L:4D, but there was no detectable influence of the short photoperiod on reproductive function.

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R. E. FALVO, A. E. BUHL, T. J. REIMERS, G. R. FOXCROFT, MARY HUNZICKER DUNN and P. J. DZIUK

Summary.

To examine a possible relationship between the release of LH and increasing testosterone levels, blood samples were collected at 2-hr intervals for 24 hr from six mature rams with indwelling jugular cannulae. Although high levels of LH often preceded increases of testosterone, a consistent time relationship between these two hormones was not observed, nor was a diurnal rhythm established for either hormone. The following day, two rams were each injected intravenously with saline, 500 i.u. HCG, or 100 μg synthetic gonadotrophin-releasing hormone (Gn-RH) respectively. Immediately after the injection, blood was collected every 15 min for approximately 4 hr. After Gn-RH, the plasma LH rose 25- to 50-fold within 12 min and was elevated for more than 3 hr. A twofold rise of plasma testosterone followed this increase of LH and testosterone remained high until the end of the experiment. After HCG treatment, the level of testosterone rose threefold within 30 min and did not decline during the experiment, but there was no effect on the LH level. Saline treatment did not influence levels of LH or testosterone.

It was concluded that daily fluctuations of testosterone and LH may occur independently, and no pattern is common to all rams. Treatment with Gn-RH results in a rise in both the testosterone and LH levels, but only testosterone is affected by HCG.