1. These studies were aimed at elucidating some of the endocrinological factors controlling metabolism in the upstream migrating stage of the life cycle of the river lamprey, L, fluviatilis, 2. Both subtotal and total extirpation of the islet tissue has been carried out. Blood glucose levels remain substantially unaffected in subtotal isletectomy, but in total extirpation of the islet tissue these rose to a mean level of 283 mg / 100 ml compared with a control value of 52 mg / 100 ml. 3. Insulin values for totally isletectomised animals 6 days after operation were about half those of controls. 4. Comparisons of the glucose tolerance curves for intact and totally isletectomised animals indicate that the operated animals have completely lost the ability to regulate blood glucose levels and that the return toward baseline values after 24 hr can probably be accounted for by urine losses. 5. The time course of the circulating levels of insulin after a single injection of glucose indicated significantly elevated values 8 and 24 hr after injection but not 2 hr after injection. Significant elevations of insulin levels were also observed after twice daily glucose loading for 12 days. 6. Hyperglycaemia has been demonstrated in lampreys subjected to a reduced oxygen tension of 20% air saturation for periods of up to 14 days. Maximum blood sugar values were recorded after 7 days hypoxia (mean 92.1 +/- 30.9 mg/100 ml) compared with a mean value of 44.5 +/- 2.3 mg/100 ml for controls. Similar tests over 7 days on hypophysectomised animals failed to show significant changes in glycaemia. 7. Circulating insulin values were reduced after adrenalin administration. Marked hyperglycaemia was also observed after injections of adrenalin. 8. After 7 days hypoxia, slight vacuolization occurred in the islet tissue of only a few of the experimental animals, but at 14 days all showed extensive hydropic degeneration affecting the light cells. Equally severe lesions were also seen in all the hypophysectomised animals after only 7 days hypoxia, but did not appear in any of the control series that had been hypophysectomised 1-2 months previously and maintained under normal oxygen tensions. 9. Measurements of nuclear diameters of islet cells showed marked increases in nuclear volumes after 24 hr of glucose loading or after adrenalin injections, but not after hypoxia treatment. 10. Increased nuclear volumes were recorded in chromaffin tissue in the earlier stages of hypoxia and after glucose loading, but were not observed in hypophysectomised animals. No nuclear enlargement was seen in the interrenal tissue under hypoxic conditions, but a slight increase in mean volumes occurred after glucose loading. In adrenalin injected animals, nuclear hypertrophy was very pronounced, probably accompanied by hyperplasia. 11. Glucagon-like immunoreactivity in the intestine has been confirmed by radioimmunoassay.
|Date of Award||1976|