Seasonal variations in oviductal activity, extensibility, and tensile strength in Chrysemys picta.

In vivo and in vitro myometrial activity, tissue extensibility, and tensile strength were measured during the annual cycle of the female turtle Chrysemys picta. Contractile rate, in vivo and in vitro, increased to a maximum in the periovulatory period, but contractile strength in vitro was inversely proportional to rate, being least in the periovulatory period. Initial oviductal circumference was highest in April and lowest in September. Although extensibility varied little, this parameter was inversely proportional to the initial circumference. Tensile strength was greatest in midwinter and least in postovulatory animals. The results are discussed in relationship to the known seasonal endocrine cycle and suggest important hormonal (estrogen, progesterone) effects upon egg retention and egg laying in this species.