Vasoactive intestinal polypeptide-like immunoreactivity and effects of VIP in the swimbladder of the cod,Gadus morhua

Abstract

1. Immunohistochemistry has been used to localize the presence of vasoactive intestinal polypeptide (VIP)-like immunoreactivity (IR) in different parts of the swimbladder and in the coeliac and swimbladder arteries of the cod,Gadus morhua. The effects of exogenous porcine VIP on the swimbladder have been studied in a perfused gas gland preparation and on isolated strips from the secretory mucosa (including the muscularis mucosae), the oval edge and the coeliac and swimbladder arteries. 2. VIP-like IR was present in nerve fibres in the muscularis mucosae and submucosa of the swimbladder wall, the oval edge region, the swimbladder artery and the coeliac artery (Figs. 1–5). No VIP-like IR was encountered in the gas gland of the swimbladder. A few IR fibres were seen in the extrinsic nerves supplying the swimbladder (Fig. 6). 3. VIP (10−7 M) in the perfusion fluid increased the flow through the gas gland of the swimbladder perfused in situ (Fig. 8), and isolated strips of the coeliac and swimbladder arteries showed a small decrease in tension in response to prolonged exposure to VIP. VIP also produced a slowly developing, profound decrease in tension of isolated strips of the secretory mucosa and the oval edge of the swimbladder (Fig. 7). 4. It is concluded that a functional innervation by VIP-containing and-releasing nerves may exist in the swimbladder and swimbladder arteries of the cod.