Empty Silastic Capsules Research Articles

Antigonadal effect of melatonin in pinealectomized and intact male hamsters.

2 studies were performed in order to determine whether exogenous melatonin can inhibit gonadal activity independently from the pineal gland. In Experiment 1, complete testicular atrophy was induced by exposing male golden hamsters to a nonstimulatory photoperiod (LD 6:18). Animals were either sacrificed and testes weight determined, or sham-pinealectomized (intact) or pinealectomized (Px) and implanted with empty or melatonin-filled Silastic capsules (25, 100, or 300 mm long). Animals were then moved to stimulatory LD 14:10 and sacrificed 45 days later. In a 2nd study, 10-week-old male hamsters maintained on LD 14:10, were either left intact of PX and implanted with melatonin-filled 300 mm Silastic capsules. At surgery 5 animals were sacrificed and paired testes weight determined. LD 6:18 resulted in complete testicular regression. Transfer from LD 6:18 to LD 14:10 resulted in the expected testicular weight increase. Testicular growth occurred to the same degree in intact and Px hamsters receiving empty Silastic capsules. Photo-induced testicular recrudescence was prevented or supressed in both intact and Px animals at all doses. Melatonin-treated hamsters had significantly smaller testes (p less than .01) than intact and Px hamsters receiving empty capsules. In the 2nd study melatonin provoked testicular atrophy in sexually mature intact and Px maintained at LD 14:10. It is suggested that the antigonadal action of melatonin occurs by means other than the pineal gland.

Effect of photoperiod length on feedback sensitivity to estradiol in the female rat.

The effect of photoperiod on the negative feedback effect of estradiol on LH release was examined in this study. Female ARS/Sprague-Dawley rats were exposed to lighting schedules of 2, 8, 16 or 22 h of light per 24 h from 60 days of age until autopsy. After 5 to 6 weeks of acclimatization to the photoperiod, all rats were ovariectomized, given various treatments during the next 14 days and sacrificed on the 15th day. Treatments consisted of either daily injections of various doses of estradiol benzoate (EB) in sesame oil or of implantation of a Silastic capsule containing crystalline estradiol-17<i>β </i>(E₂) at the time of ovariectomy; in addition to untreated controls in each group, some animals received either oil injections or implantation of an empty Silastic capsule, as appropriate. At the time of autopsy, blood was taken for radioimmunoassay of serum LH and body and uterine weights were recorded. Untreated ovariectomized rats, and those receiving oil injections or an empty capsule implant, showed wide variations in serum LH levels; no significant effect of photoperiod length could be demonstrated. At low dose ranges of EB, very little effect on serum LH was seen. A dose-related effect was seen on relative uterine weight, and the response to EB was significantly greater (p < 0.05) in the 22 h photoperiod than in the others, but this effect was not seen at moderate or at presumptively high doses of estradiol. At these higher doses, however, there was a significant effect of photoperiod length on serum LH levels (p < 0.05). In both of these dose ranges, the longer the photoperiod, the higher the LH level at any given dose of estrogen. These results suggest that photoperiod length can alter the sensitivity of the LH control system to the negative feedback effects of estrogen: in the case of the rat, the shorter the photoperiod, the more sensitive the negative feedback system.

Maintenance of spermatogenesis in rats with intratesticular implants containing testosterone or dihydrotestosterone (DHT).

Silastic capsules containing testosterone or dihydrotestosterone (DHT) were implanted into the left testis of adult hypophysectomized rats and the animals were autopsied at the interval of 1, 2, 4, and 8 weeks. At 4 and 8 weeks, testes containing DHT or testosterone implants were heavier than contralateral control testes or gonads implanted with empty silastic capsules. Advanced stages of spermatogenesis were observed adjacent to implants containing testosterone or DHT at 4 or 8 weeks, but were absent in the contralateral testes or testes implanted with empty capsules. These results indicate that DHT is capable of maintaining spermatogenesis in the hypophysectomized rat.