The effects of hypoxia on blood sugar levels and on the endocrine pancreas, interrenal, and chromaffin tissues of the lamprey, Lampetra fluviatilis (L.)

Abstract

Hyperglycaemia has been demonstrated in river lampreys ( Lampetra fluviatilis) 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 hypophy-sectomised animals failed to show significant changes in glycaemia. Marked hyperglycaemia was also observed after injections of adrenalin. No significant changes in liver glycogen concentrations occurred after periods of hypoxia. After 7 days hypoxia, slight vacuolisation 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. Vacuolisation also occurred in only a small proportion of the animals subjected to daily glucose loading over a 8–11 day period, but was not seen after shorter periods of adrenalin administration. 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. Aldehyde-fuchsinophil granulation of the dark cords was reduced after glucose loading, but was still retained by the cells of the dark cords after hypoxia treatment. Marked differences have been recorded in the mean nuclear volumes of light and dark cells and, although both respond to glucose loading, the increases in nuclear size tended to be greater in the light cells. Stimulation of mitotic division has been seen in hypoxia, glucose loading, and especially after exogenous adrenalin treatment, but is apparently confined to light cell lobules. The histological observations and nuclear measurements are consistent with the view that both light and dark cells may be regarded as developmental stages in a single β-cell-type. 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. Although hypophysectomy inhibits the hyperglycaemic and behavioural responses to hypoxia, it does not prevent the hydropic degeneration of the islet tissue. While there is some evidence for a pituitary influence on chromaffin tissue activity, it remains in doubt whether this is mediated through glucocorticoid activity of the interrenal tissue.