The golden hamster responds to a short photoperiod (less than 12.5 hours light/day) by collapse of its reproductive system. Levels of serum LH, FSH, PRL and testosterone fall, and testis size and function decline dramatically after about 6-12 weeks of short-day exposure. Increased sensitivity of the hamster to negative feedback of androgen is also present during this period. From about 12-24 weeks of short days, the reproductive system recrudesces to the viable state present before collapse. When this process occurs while the animal is maintained on short days, it is triggered endogenously and called spontaneous recrudescence. The present study focused on recrudescence onset by examining 2 hypotheses: (1) recrudescence is triggered by attainment of a certain duration when androgen levels exist below a threshold; therefore animals receiving high androgen doses should have a greater delay in recrudescence than animals given a low dose, and (2) onset of recrudescence is delayed by blocking PRL release These hypotheses were tested in 83 male golden hamsters exposed to only 6 hours of light per day. Experimental groups were manipulated by implanting sc high or low doses of testosterone propionate (TP) contained in Silastic capsules, or by varying durations of TP implantation, or by injecting CB-154 (2-bromo-(alpha)-ergocryptine), which inhibits PRL release. The control group received empty capsules. At the beginning of the short photoperiod and about every 3 weeks thereafter, animals were anesthetized and weighed, the length and width of the right testis was measured, and blood samples were drawn. Serum FSH, LH and PRL were assayed by radioimmunoassay. The stress accompanying repeated surgery was examined by measuring some experimental groups at only 3 instead of 8 different times. Onset of recrudescence among the groups was compared by evaluating the (1) actual values of testis index, FSH, LH and PRL during recrudescence, (2) period from the lowest value to the value showing first significant rise, (3) week of the first significant rise of a measurement, and (4) slope of values of a measurement over a period of recrudescence During spontaneous recrudescence in the control group, serum FSH increased first, at about 15 weeks, followed at 18 weeks by increases in serum LH and PRL and testis index (TI), length x width of right testis/body weight. In general, the groups receiving androgen displayed earlier, rather than later, recrudescence than did the control group without androgen. The group receiving CB-154 showed an initiation time and pattern of recrudescence similar to those of the control group. When one androgen-exposed group differed from another in onset of reproductive parameters, an earlier increase in TI correlated highly with an earlier increase in PRL but poorly with an earlier increase in FSH or LH. In a related finding, those groups with androgen which showed onset of recrudescence faster than the control group or other androgen-treated group, also displayed surges of serum PRL during capsule implantation. In addition, comparison of two of the groups receiving androgen showed that while both TI and PRL increased faster in one than the other, LH did not Three conclusions were drawn from these data: (1) androgen implanted for a short time (week 7-8 or 6-8 of a short photoperiod) advances recrudescence, not by affecting the measurement of duration of low androgen levels, but probably by stimulating PRL release. (2) PRL may be capable of advancing the onset of testicular recrudescence in the absence of a rise in serum LH levels, perhaps by increasing the ratio of LH receptors to available LH, and (3) PRL increases involved in earlier recrudescence are probably not physiological / acase@tulane.edu
| Identifer | oai:union.ndltd.org:TULANE/oai:http://digitallibrary.tulane.edu/:tulane_23364 |
| Date | January 1980 |
| Contributors | Fishback, James Brian (Author) |
| Publisher | Tulane University |
| Source Sets | Tulane University |
| Language | English |
| Detected Language | English |
| Rights | Access requires a license to the Dissertations and Theses (ProQuest) database., Copyright is in accordance with U.S. Copyright law |
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