6. ADRENAL STEROIDS AND ACTH
347
A comparison of the effects of exogenous cortisol administration with
those of experimental starvation is informative. Thus after 8 days of starvation in the goldfish there was 15% loss in body weight, caused almost
entirely by a loss in parietal muscle. There was no apparent change in
composition of the muscle. Cortisol injection for 4 days induced a similar
weight loss and also had no effect on muscle composition. The amount of
tissue water lost may be related to the extra potassium lost under both
conditions, and the amounts are similar to those anticipated from the ratio
of potassium to water in the intracellular fluid compartment (Stimpson,
1965; Storer, 1967).
There are many features of corticosteroid-liver interactions which are
unknown at present. So far, fish liver has not been observed to increase
in size after corticosteroid treatment. Hepatic enzyme induction by corticosteroids also differs in fishes when compared to other vertebrates (S. K.
Chan and Cohen, 1!364). The liver of the eel appears to play a role of
equivalent nature to that of mammals, except that there is less emphasis
on amino acid deamination ( Kenyon, 1967).
There are data from teleosts that do not fit into the usual pattern
extrapolated from mammalian work. Thus, in Fundulus heteroclitus,
Poecilia formosa, and P. latipinnu the liver increases in size after hypophysectomy (Pickford and Atz, 1957; Ball et al., 1965; Ball, 1963) and
remains enlarged even during 9 days of starvation in P. latipinnu (Ball,
1968). The enlarged liver of hypophysectomized P. latipinnu is reduced
in weight by cortisol or ACTH treatment but not by GH or TSH (Ball,
1968), and GH is also inffective in F. heteroclitus (Pickford, 1953). These
findings contrast with data from mammals, in which corticosteroids increase liver size (Chester Jones and Bellamy, 1964).
Hypophysectomy in P. latipinnu also increases liver glycogen content
(as per cent liver wet weight), and this elevated glycogen store is maintained above normal during a 9-day fast (Ball et al., 1966a). Fasting
reduced liver glycogen in intact fish by about 50% but only by 18% in
hypophysectomized fish, which suggests a pituitary factor that enhances
glycogenolysis. This idea is borne out by results of replacement treatment
of hypophysectomized P. latipinnu: ACTH or cortisol reduced both liver
weight and liver glycogen (Ball et al., 1966a; Ball, lWB), but the fall in
glycogen could account for only about 16% of the reduction of liver weight
by ACTH (Ball, 1M). Growth hormone, prolactin, and TSH had no
effect on liver glycogen in hypophysectomized P . latipinna (Ball et aZ.,
1!%6a; Ball, 1968), suggesting that ACTH and cortisol might physiologicaliy promote glycogenolysis in this species.
Working with intact Tilapia mssambica, Swallow and Fleming
(1986) found that ACTH injected into short-term fasted fish produced
347
A comparison of the effects of exogenous cortisol administration with
those of experimental starvation is informative. Thus after 8 days of starvation in the goldfish there was 15% loss in body weight, caused almost
entirely by a loss in parietal muscle. There was no apparent change in
composition of the muscle. Cortisol injection for 4 days induced a similar
weight loss and also had no effect on muscle composition. The amount of
tissue water lost may be related to the extra potassium lost under both
conditions, and the amounts are similar to those anticipated from the ratio
of potassium to water in the intracellular fluid compartment (Stimpson,
1965; Storer, 1967).
There are many features of corticosteroid-liver interactions which are
unknown at present. So far, fish liver has not been observed to increase
in size after corticosteroid treatment. Hepatic enzyme induction by corticosteroids also differs in fishes when compared to other vertebrates (S. K.
Chan and Cohen, 1!364). The liver of the eel appears to play a role of
equivalent nature to that of mammals, except that there is less emphasis
on amino acid deamination ( Kenyon, 1967).
There are data from teleosts that do not fit into the usual pattern
extrapolated from mammalian work. Thus, in Fundulus heteroclitus,
Poecilia formosa, and P. latipinnu the liver increases in size after hypophysectomy (Pickford and Atz, 1957; Ball et al., 1965; Ball, 1963) and
remains enlarged even during 9 days of starvation in P. latipinnu (Ball,
1968). The enlarged liver of hypophysectomized P. latipinnu is reduced
in weight by cortisol or ACTH treatment but not by GH or TSH (Ball,
1968), and GH is also inffective in F. heteroclitus (Pickford, 1953). These
findings contrast with data from mammals, in which corticosteroids increase liver size (Chester Jones and Bellamy, 1964).
Hypophysectomy in P. latipinnu also increases liver glycogen content
(as per cent liver wet weight), and this elevated glycogen store is maintained above normal during a 9-day fast (Ball et al., 1966a). Fasting
reduced liver glycogen in intact fish by about 50% but only by 18% in
hypophysectomized fish, which suggests a pituitary factor that enhances
glycogenolysis. This idea is borne out by results of replacement treatment
of hypophysectomized P. latipinnu: ACTH or cortisol reduced both liver
weight and liver glycogen (Ball et al., 1966a; Ball, lWB), but the fall in
glycogen could account for only about 16% of the reduction of liver weight
by ACTH (Ball, 1M). Growth hormone, prolactin, and TSH had no
effect on liver glycogen in hypophysectomized P . latipinna (Ball et aZ.,
1!%6a; Ball, 1968), suggesting that ACTH and cortisol might physiologicaliy promote glycogenolysis in this species.
Working with intact Tilapia mssambica, Swallow and Fleming
(1986) found that ACTH injected into short-term fasted fish produced