Role of islet tissue in the cold‐induced hyperglycemia of the killifish, Fundulus heteroclitus

Abstract

Islet tissue histology and serum glucose concentrations were examined in salt-water-adapted killifish, Fundulus heteroclitus, acclimated to 20°C and to -1.5"C for one and ten days. Exposure to subzero temperatures produced a hyperglycemia accompanied by hypertrophy and degranulation of alpha cells in the islets and by atrophy of the islet beta cells with no changes in granulation. The cold-induced hyperglycemia presumably resulted from an increase in circulating levels of glucagon and from a failure of the beta cells to release insulin.Exposure to subzero temperatures elicits a marked hyperglycemia in the killifish, Fundulus heteroclitus, which persists for several weeks (Umminger, '69, '70). This cold-induced hyperglycemia results from a breakdown of hepatic glycogen (Umminger, '70) produced by a n increase in the specific activity of hepatic glycogen phosphorylase (Benziger and Umminger, '72). Previous studies have demonstrated that the hormonal regulation of this hyperglycemic response is not under pituitary control and the suggestion has been made that the pancreatic islets are probably involved (Umminger, '71, '72). The present investigation provides histological evidence that the islets of the killifish are indeed implicated in the elicitation of the cold-induced hyperglyceniia. MATERIALS AND METHODSAdult male F. heteroclitus were obtained by air freight from the Supply Department of the Marine Biological Laboratory in Woods Hole, Massachusetts, on October 27, 1970. The fish were subsequently maintained under a regime of 12 hours of light per day i n Instant Ocean aquaria (salinity 33"/00) at the University of Cincinnati. The killifish were fed daily ad libitum with Rangen's Quality Trout Feed, but were not fed the day of autopsy. One group of five fish was kept at 20°C for 52 weeks. A second group of five fish was maintained at 10°C for 28 weeks and at 5°C for 24 weeks; at the end of this acclimation period, the fish were transferred to a cold room held at -1.5"C and the water at 5°C was allowed to cool gradually to -1.5"C in six hours; the fish remained at -1.5" C for one day before autopsy. A third group of three fish was maintained at 10°C for 28 weeks, at 5°C for 24 weeks and at -1.5"C for ten days.At autopsy, the tails of fish lightly anesthetized with tricaine methanesulfonate (MS 222) were severed and the free-flowing blood was collected from the caudal artery in microhematocrit tubes. The blood was allowed to clot before centrifugation and the serum from individual fish was stored in tightly corked vials at -20°C. The following day the samples were briefly thawed for withdrawal of microliter samples of serum for the chemical deterniination of glucose. Serum glucose was determined using a n ultramicro adaptation (Pickford et al., '69) of the Glucostat (Worthington Biochemic a1 Corp .) enzymatic method, following the procedure of Saifer and Gerstenfeld ('58).The large principal islets (Brockmann bodies) at the base of the gallbladder near the cystic duct were fixed i n Bouin's fluid at the t...

Effect of low temperature on development of the coccidium Eimeria funduli in the Gulf killifish

“…In fact, another host, F. heteroclitus from the Atlantic U.S. coast, survives in supercooled water ( -1-5 °C) by good ionic regulation and hyperglycemia. Whether infected killfish survive supercooled temperatures deserves investigation because hormonal control of the cold-induced hyperglycemia is apparently under the control of islet cells of the pancreas (Umminger & Bair, 1973). Stressed fish avoid harsh conditions (low salinity; low temperature), if possible.…”