5. THE ENDOCRINE PANCREAS
297
a seasonal cycle. Also, Falkmer (1961) did not see seasonal variations in
the marine teleost Cottus scorpius. Maske et a2. (1956) obtained higher
yields of insulin and zinc from the Brockmann bodies of Pleuronectidae
in December than in April; they explain this with the change in nutritional
conditions.
It appears difEcult to interpret these differing findings. Possibly, the
interaction of local factors (such as temperature and food supply) with
the life cycle of a species plays a role. In some cases, increased food intake
and growth during summer may lead to a high seasonal requirement of
insulin; in other cases, when animals are active also in winter (e.g., S a l m
trutta), the insulin requirement may be similar at all seasons.
3. ISLET CHANGES AND MIGRATION
Islet hyperplasia occurs both in Pacific salmon, Oncorhynchus nerka
(Robertson and Wexler, 1960; McBride, 1967), and in the rainbow trout,
Salmo gairdneri (Robertson et aZ., 1961), during the anadromous spawning migration, but it is also found in catadromous eel, Anguillu japonica,
from the depth of the Japan Sea (Honma, 1966). Nevertheless, islet
hyperthrophy occurs in spawning nonmigratory rainbow trout ( Robertson
et al., 1961).
B. Experimental Islet Studies
1. HYPERPHAGIA AND STARVATION
According to Hess ( 1935), reduction of the number of islets can be
induced in the rainbow trout, Salmo irideus, by (1) addition of fat or fat
and carbohydrate to the diet, (2) overeating, and (3) lack of muscular
activity. The greatest reduction of islets was observed after addition of
fat and carbohydrate to the diet; overeating led to a greater reduction of
islets than the lack of exercise. Higher islet counts were obtained by
feeding beef liver than with either pig spleen or beef heart. Baron (1934)
finds no changes in the islets of starving sticklebacks, Gusterosteus
aculeatus. Starvation causes a reduction of islet size in the eel, Anguillu
anguilla (Palayer, 1WZ).
2. GLUCOSE ADMINISTRATION
a. Glucose Tolerance. Whereas Young and Chavin (1965) report a
short mammalianlike response to glucose injections in goldfish, Carassius
auratus, kept at a rather high temperature ( WOC), all other investigators
observed a rather slow return to normal levels after glucose injections in
297
a seasonal cycle. Also, Falkmer (1961) did not see seasonal variations in
the marine teleost Cottus scorpius. Maske et a2. (1956) obtained higher
yields of insulin and zinc from the Brockmann bodies of Pleuronectidae
in December than in April; they explain this with the change in nutritional
conditions.
It appears difEcult to interpret these differing findings. Possibly, the
interaction of local factors (such as temperature and food supply) with
the life cycle of a species plays a role. In some cases, increased food intake
and growth during summer may lead to a high seasonal requirement of
insulin; in other cases, when animals are active also in winter (e.g., S a l m
trutta), the insulin requirement may be similar at all seasons.
3. ISLET CHANGES AND MIGRATION
Islet hyperplasia occurs both in Pacific salmon, Oncorhynchus nerka
(Robertson and Wexler, 1960; McBride, 1967), and in the rainbow trout,
Salmo gairdneri (Robertson et aZ., 1961), during the anadromous spawning migration, but it is also found in catadromous eel, Anguillu japonica,
from the depth of the Japan Sea (Honma, 1966). Nevertheless, islet
hyperthrophy occurs in spawning nonmigratory rainbow trout ( Robertson
et al., 1961).
B. Experimental Islet Studies
1. HYPERPHAGIA AND STARVATION
According to Hess ( 1935), reduction of the number of islets can be
induced in the rainbow trout, Salmo irideus, by (1) addition of fat or fat
and carbohydrate to the diet, (2) overeating, and (3) lack of muscular
activity. The greatest reduction of islets was observed after addition of
fat and carbohydrate to the diet; overeating led to a greater reduction of
islets than the lack of exercise. Higher islet counts were obtained by
feeding beef liver than with either pig spleen or beef heart. Baron (1934)
finds no changes in the islets of starving sticklebacks, Gusterosteus
aculeatus. Starvation causes a reduction of islet size in the eel, Anguillu
anguilla (Palayer, 1WZ).
2. GLUCOSE ADMINISTRATION
a. Glucose Tolerance. Whereas Young and Chavin (1965) report a
short mammalianlike response to glucose injections in goldfish, Carassius
auratus, kept at a rather high temperature ( WOC), all other investigators
observed a rather slow return to normal levels after glucose injections in