GENERAL AND COMPARATIVE ENDOCRINOLOGY 51, 11-83 (1983) Adrenergic Inhibition of Uterine Contractions and Oviposition in the Lizard Anolis caroiinensis RICHARD E. JONES, CLIFF H. SUMMERS, AND KRISTIN H. LOPEZ Laboratory of Comparative Reproduction, Department of Environmental, Population, and Organismic Biology, University of Colorado, Boulder, Colorado 80309 Accepted August 5, 1982 Injection of arginine vasotocin (AVT), which induces oviposition in several lizard species, fails to do so in Anolis carolinensis. We tested the hypothesis that epinephrine-induced activation of l3-adrenoreceptors in the uterus inhibits AVT action on uterine smooth muscle. Pretreatment of gravid females with the P-adrenoreceptor antagonist dichloroisoproterenol 15 min before an AVT injection resulted in uterine sensitivity to AVT and subsequent oviposition. Furthermore, in vitro tests indicated that epinephrine as well as a P-adreno- receptor agonist (isoproterenol) inhibit uterine tonic and rhythmic contractions that nor- mally follow exposure to AVT. These results suggest that stress-induced secretion of epi- nephrine can act as a short-term inhibitor of oviposition in this species. Many reptiles are known to delay ovi- position when adverse environmental con- ditions prevail, thus avoiding deposition of eggs in a nest microhabitat that is not con- ducive to embryonic survival (Tinkle and Gibbons, 1977; Guillette et al., 1980). We propose here a physiological mechanism, involving interaction of stress and the hor- mone arginine vasotocin, whereby such a delay in egg-laying could occur. Arginine vasotocin (AVT), a hormone secreted by the neurohypophysis of lizards (Sawyer, 1977), is a potent stimulator of uterine (oviductal) contractions. If a low dosage of AVT is in- jected into pregnant viviparous lizards, par- turition soon occurs (Guillette, 1979; Guil- lette and Jones, 1982). Similarly, oviposi- tion is induced by AVT injection in several oviparous lizards (Guillette and Jones, 1982). In previous experiments, however, we failed to induce oviposition with AVT in the lizard An& carolinensis, regardless of dosage (Guillette and Jones, 1982). This lizard alternates ovulation of a single egg from each ovary every 14 days during the breeding ‘season, and thus oviposition of an egg oc&rs alternately from each uterus. A few days before unilateral oviposition of a shelled egg, a new egg is ovulated into the contralateral uterus. The resultant “two- egg” condition lasts 4 to 5 days. After ovi- position, the “one-egg” condition lasts for about 10 days (Hamlett, 1952). Near the time of oviposition, the uterus contralateral to the one contracting remains relaxed be- cause the secretory corpus luteum in the ipsilateral ovary locally inhibits AVT-in- duced uterine contraction (Jones et @I., 1982). The uterus that would be the next one to contract in the cycle responds in v&u to AVT, but as mentioned above, fails to respond after an injection of AVT. Inas- much as the mammalian uterus relaxes upon exposure to epinephrine or p-adrenore- ceptor agonists due to activation of p-ad- renergic receptors (Wansbrough et al., 1968: Johansson and Andersson, 198Q),‘we tested the hypothesis that epinephrine i*~biti~~ of AVT-induced uterine contraction, by ac- tivation of @adrenoreceptors in uterine smooth muscle, explains why A,nolis fails to oviposit in response to exogenous AVT. MATERIALS AND METHODS Experiment I. In an initial experiment, we selected 38 Anolis females, each with a single uterine egg. 77 0016-6480183 $1.50 Copyright @I 1983 by Academic Press. Inc. AU rights of reproduction in any form reserved.