The effects of subtotal and total isletectomy in the river lamprey, Lampetra fluviatilis

Abstract

Measurements on the islet tissue of the lamprey indicate that in relation to body weight the total volume is similar to that of the hagfish, Myxine glutinosa, and to the ratio of islet volume to body weight derived for human islet tissue. Separate estimates for the volumes of cranial and caudal islet tissue show that in Lampetra fluviatilis, the latter is approximately twice the volume of the cranial component, whereas in the nonparasitic species L. planeri, the two regions are similar in size. Both subtotal and total extirpation of the islet tissue has been carried out in L. fluviatilis, the former operation involving removal of either the caudal or cranial islet regions. 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. Liver glycogen values were in general too variable to permit definite conclusions, but significant decreases were noted in animals subjected to caudal isletectomy. 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. Measurements of nuclear diameters of islet cells in glucose loaded animals show that after a single glucose injection of 100 mg the volume of the nucleus still remains much larger than those of the controls, 24 hr after the injection. Similar increases in nuclear volumes were observed in animals receiving repeated injections over periods of 8–11 days. In partial isletectomy there was compensatory hypertrophy of the nuclei of the remaining islet cells which tended to be more marked in the cranial region after removal of the caudal lobe. Vacuolisation and marked degranulation of islet cells has been observed only in the cranial region of caudally isletectomised animals. These observations are interpreted as an indication of the continuing physiological demand for insulin in the fasting migratory stage of the river lamprey and the retention of an important role for this hormone in carbohydrate metabolism.