Effect of pregnancy on gallbladder contractility in the guinea pig.

The effect of pregnancy on the in vitro contractility of the guinea pig gallbladder was examined by stimulating tissues from pregnant and nonpregnant guinea pigs with acetylcholine, cholecystokinin-octapeptide, and elevated extracellular potassium. Pregnancy was characterized by significant decreases in the magnitude of the contractile responses to acetylcholine and cholecystokinin-octapeptide at each point along their respective dose-response curves. The decrease in tension development was not associated with any change in the sensitivity of the gallbladder to either of the agonists. The contractile response to increased extracellular potassium was unaffected by pregnancy. This latter point suggests that pregnancy is not characterized by a generalized decrease in gallbladder smooth muscle contractility, but rather that it may affect a step in the excitation-contraction coupling process common to acetylcholine and cholecystokinin-octapeptide stimulation. The data suggest that the sluggish behavior of the gallbladder in vivo during pregnancy may be due to a decrease in the magnitude of the contractile responses to cholinergic and hormonal stimulation.