Effect of ovarian hormone pretreatment on gallbladder motility in vitro

Adult male guinea pigs were pretreated with estrogen, progesterone, or estrogen plus progesterone and the $\text{in vitro}$ contractile response of the gallbladder to cholinergic stimulation examined. The data were compared with results obtained from control animals. Progesterone pretreatment was associated with a significant decrease in the maximal contractile response of the tissues and with a significant increase in the dose of acetylcholine needed to produce a threshold response. Estrogen pretreatment significantly decreased the threshold dose requirements but had no effect on maximum tension development. In addition, estrogen pretreatment antagonized the inhibitory effect of progesterone pretreatment. The data support the hypothesis that the ovarian steroid hormones can affect gastrointestinal smooth muscle. Furthermore, the hormones appear to exert independent and opposite effects on gallbladder motility. Additional studies will be required to determine the physiological significance of these observations.