Stimulus requirements for pregnancy initiation in the golden hamster (Mesocricetus auratus) change with age and parity.

Hamsters were mated repeatedly at 60, 180, 300 and 420 days of age or once during their lifetime at one of these ages. Copulatory stimulation was varied both for number of ejaculations (2 versus 14) and amount of vaginocervical stimulation (5 versus 50-60 intromissions). Two ejaculations provided sufficient spermatozoa to maximize litter size for all age and parity classes tested. Differences in fecundity depended on the amount of vaginocervical stimulation received. Higher levels of vaginocervical stimulation increased littering success at 300 and 420 days for nulliparous females and at 180, 300 and 420 days for multiparous females. Females which did not deliver litters did not show a cessation of oestrous cycles which characteristically follows the induction of a luteal phase. The decreased fecundity observed with increasing age or parity therefore resulted from a change in sensitivity to the stimulus conditions necessary to activate the neuroendocrine arc for establishment of pregnancy.

Mating-induced inhibition of receptivity in the female golden hamster (Mesocricetus auratus): III. Stimuli mediating long-term effects.

In the golden hamster, mating with an intact male results in both a reduction in receptivity shown toward a second male (short-term effect) as well as an absolute abbreviation of the receptive period (long-term effect). The present study examined the components of the mating situation responsible for the long-term effect. In experiment 1 we showed that the paradigm used to determine receptivity (i.e., brief hourly exposures to an intact male) did not affect the duration of receptivity whereas an ad lib mating early during the receptive period resulted in a 40% reduction in the length of behavioral estrus. In experiment 2 females received various types of mating stimuli, e.g., mounts from an apronned male, intromissions from a vasectomized male, a simulated copulatory plug, manually-induced lordosis, or several of these stimuli in combination. Only intromissions from an intact or vasectomized male significantly reduced the duration of behavioral estrus. Although as few as 10 intromissions from a vasectomized male were effective in significantly shortening the receptive period, higher levels of vaginocervical stimulation from a single male (experiment 3) or from additional males (experiment 4) effected significantly greater reductions in the length of behavioral estrus. Our results further demonstrated that only those females that subsequently became pseudopregnant showed significant abbreviations of behavioral estrus. The association of these two phenomena is of obvious adaptive value since it provides a mechanism to terminate a behavior once its function has been achieved.

Metabolic disposition of radioactive phenothiazine in calves: a balance study.

Three Charolais calves were treated orally with [14C] phenothiazine. The amount of radioactivity excreted in the urine and feces was measured. The average quantity of the excreted dose recovered was divided equally between the urine and the feces. The radioactivity found in the feces and gastrointestinal tract was variable between the animals, but the urinary radioactivity was constant. Only a small amount of the administered dose was retained by selected organs, with the liver and kidneys accounting for most of that amount. These organs also had tissue-to-blood ratios of radioactivity greater than unity, whereas the other tissues had ratios close to unity. Essentially complete recovery of the administered radioactive dose was achieved.