5. THE ENDOCRINE PANCREAS
305
well as the measurement of endogenous insulin under various natural
and experimental conditions may become indispensable.
2. GLUCAGON
In Lumpetru fluviatilis, glucagon injections had no initial effect, but
after a delay of 4 hr decreased the blood glucose level (Bentley and
Follett, 1965). In Mydine glutinosu, glucagon had no effect at all (Falkmer and Matty, 1966a). In chondrichthyans, high doses of glucagon may
produce a slight hyperglycemia ( W. C. Grant, Jr., 1964; Patent, 1968).
Teleosts respond to glucagon with hyperglycemia (Wright, 1958; Falkmer, 1961; Tashima and Cahill, 1964; Falkmer and Matty, 1966b; Young
and Chavin, 1965). However, since species specific glucagon was much
more effective than ox glucagon in Cottus scorpius (Falkmer, 1966), the
specificity of the hyperglycemic effect of mammalian glucagon in fishes is
difficult to assess. Hyperglycemia is easily evoked by many factors. When
given to toadfish tissues in uitro, glucagon caused no changes in glucose
metabolism in heart or skeletal muscle. In the liver, it (1) depressed conversion of glucose into total lipids and CO, ( 2 ) increased conversion of
glucose into glycogen, (3) stimulated liver glycogenolysis at the same
time, and (4) from acetate or alanine it stimulated gluconeogenesis
(Tashima and Cahill, 1964).
As in the case of insulin, the available experimental data do not yet
permit to draw conclusions on the physiological role of glucagon in fishes.
V. SUMMARY
( 1) Insulin, or a biologically and immunologically similar substance,
has been found in protostomians and nonvertebrate deuterostomians. B
cell-like elements have been seen in the gastrointestinal tract of some of
the species.
(2) In cyclostomes, endocrine and exocrine pancreas are completely
separated; the endocrine pancreas contains only two granular cell forms
( B cells, and Gomori negative granular cells of unknown function) and
agranular cells.
(3) The pancreas of all gnathostomes may have derived from a compact pancreas, with endocrine cells appearing first as an outer layer of
small ducts. This picture is found only in some elasmobranchs; in other
elasmobranchs and all “higher” fishes there is a strong tendency to concentrate the endocrine pancreas as “islets.” In the actinopterygians, there
305
well as the measurement of endogenous insulin under various natural
and experimental conditions may become indispensable.
2. GLUCAGON
In Lumpetru fluviatilis, glucagon injections had no initial effect, but
after a delay of 4 hr decreased the blood glucose level (Bentley and
Follett, 1965). In Mydine glutinosu, glucagon had no effect at all (Falkmer and Matty, 1966a). In chondrichthyans, high doses of glucagon may
produce a slight hyperglycemia ( W. C. Grant, Jr., 1964; Patent, 1968).
Teleosts respond to glucagon with hyperglycemia (Wright, 1958; Falkmer, 1961; Tashima and Cahill, 1964; Falkmer and Matty, 1966b; Young
and Chavin, 1965). However, since species specific glucagon was much
more effective than ox glucagon in Cottus scorpius (Falkmer, 1966), the
specificity of the hyperglycemic effect of mammalian glucagon in fishes is
difficult to assess. Hyperglycemia is easily evoked by many factors. When
given to toadfish tissues in uitro, glucagon caused no changes in glucose
metabolism in heart or skeletal muscle. In the liver, it (1) depressed conversion of glucose into total lipids and CO, ( 2 ) increased conversion of
glucose into glycogen, (3) stimulated liver glycogenolysis at the same
time, and (4) from acetate or alanine it stimulated gluconeogenesis
(Tashima and Cahill, 1964).
As in the case of insulin, the available experimental data do not yet
permit to draw conclusions on the physiological role of glucagon in fishes.
V. SUMMARY
( 1) Insulin, or a biologically and immunologically similar substance,
has been found in protostomians and nonvertebrate deuterostomians. B
cell-like elements have been seen in the gastrointestinal tract of some of
the species.
(2) In cyclostomes, endocrine and exocrine pancreas are completely
separated; the endocrine pancreas contains only two granular cell forms
( B cells, and Gomori negative granular cells of unknown function) and
agranular cells.
(3) The pancreas of all gnathostomes may have derived from a compact pancreas, with endocrine cells appearing first as an outer layer of
small ducts. This picture is found only in some elasmobranchs; in other
elasmobranchs and all “higher” fishes there is a strong tendency to concentrate the endocrine pancreas as “islets.” In the actinopterygians, there