Actions of cholecystokinin-related peptides on the gallbladder of bony fishes in vitro.

1. Cholecystokinin (CCK) family peptides elicited dose-related gallbladder contractions in vitro for bluegill (Lepomis macrochirus), killifish (Fundulus heteroclitus), and bowfin (Amia calva). 2. Effects measured by increases in isometric contractions indicated equipotency for nonsulfated forms of CCK and caerulein (CRL; bluegill) and for sulfated CCK and CRL (bluegill, fundulus). Sulfation increased potency. 3. Responses to CCK-related peptides were insensitive to atropine, a muscarinic antagonist, which blocked acetylcholine-induced contractions, used for calibration of preparations. 4. Activity of sulfated CCK8 in bowfin, a holostean fish, suggests sensitivity of gallbladder to CCK-related intestinal hormones may be a general feature of osteichthyeans.