Reflex ovulation in light-induced persistent estrus (LLPE) rats: Role of sensory stimuli and the adrenals

Penile intromissions have been thought to be the primary stimulus for reflex ovulation in light-induced persistent estrus (LLPE) rats, even though other stimuli also trigger reflex ovulation. To clarify the nature of these noncoital stimuli, intact (nonadrenalectomized) LLPE rats were briefly exposed to a variety of environmental stimuli, other than intromissions, and checked for ova 19–22 hr later. Summary of results (number of rats ovulating/number of rats tested): (A₁) home cage ($\text{3}\text{10}$); (B₁) home cage + vaginal taping ($\text{2}\text{9}$); (C₁) home cage + male-soiled bedding ($\text{15}\text{28}$); (D₁) novel cage ($\text{2}\text{11}$); (E₁) novel cage + vaginal taping ($\text{2}\text{11}$); (F₁) novel cage + vaginal taping + male-soiled bedding ($\text{9}\text{19}$); (G₁) novel cage + vaginal taping + male-soiled bedding + male mounts without intromissions ($\text{14}\text{26}$). The percentage of LLPE rats that ovulated in the last-mentioned test condition was related to the degree of proceptivity/receptivity of the LLPE females. Eight of eight proceptive LLPE females ovulated, but only $\text{6}\text{18}$ nonproceptive females ovulated. To account for reflex ovulation in the absence of intromission it has been suggested that adrenal progesterone (P) stimulates release of an ovulatory quota of luteinizing hormone. This study demonstrates no significant differences in percentage of LLPE females ovulating in corresponding groups of adrenalectomized (ADX) and adrenal-intact females. Summary of results: A₂ = $\text{0}\text{6}$, B₂ = $\text{5}\text{15}$, C₂ = $\text{4}\text{16}$, D₂ = $\text{2}\text{14}$, E₂ = $\text{5}\text{13}$, F₂ = $\text{7}\text{19}$, G₂ = $\text{10}\text{21}$. Conclusion: (a) Exposure to a factor in male-soiled bedding induces reflex ovulation in a significant proportion of adrenal-intact LLPE animals while exposure to a novel cage and/or vaginal taping does not, (b) penile intromissions are not the primary stimulus for reflex ovulation in intact proceptive LLPE rats, and (c) adrenal P is not required for reflex ovulation after tests with noncoital stimuli.