226
J. N. BALL
planted pituitary proved capable of secreting sufficient paralactin to
maintain freshwater survival in Poecilia forrnosa (Ball and Kallman,
1962; Ball et al., 1965), P. latipinna (Ball, 1965b; Ball and Olivereau,
1965), and Xiphophorus ( Schreibman and Kallman, 1964). In P. latipinna
the paralactin from ectopic transplants maintains the normal low rate of
sodium outflux in freshwater and the low rate of sodium turnover in isotonic dilute seawater (Ball, 1968). Although it seems certain that in
cyprinodonts at least, hypothalamic connections are not essential for
secretion of paralactin at normal levels, the absence of rigorously quantitative data on rates of secretion of the hormone in grafted fish compared with normal fish precludes the assumption that a hypothalamic
paralactin-inhibiting factor exists in teleosts, particularly since prolactin
in some birds appear to be under stimulatory hypothalamic control (see
Tixier-Vidal et al., 1966; Meites and Nicoll, 1966).
11. GROWTH HORMONE
A. Introduction
Growth hormone (GH), or somatotropin (STH), is best known and
most readily characterized as the pituitary factor which promotes overall
growth of the body, even when acting in the absence of the other pituitary hormones, for example, when injected into hypophysectomized animals. Many complex actions of the hormone on metabolic processes
underlie this growth promotion, and recent accounts of these metabolic
actions of GH in mammals will be found in the reviews by Knobil and
Hotchkiss ( 1964) and Evans et al. (1966), and in the symposium edited
by Pecile and Miiller (1968). Growth hormone is known from studies in
higher vertebrates to be particularly important as a synergist with other
hormones, including among its properties for instance the power to enhance the effects of tropic pituitary hormones on their target glands
(R. W. Smith et al., 1955; Pickford and Atz, 1957; Evans et al., 1966).
Nearly all studies concerned with the physiology of GH in fishes relate to stimulation of body growth, and there is little published data on
other aspects of its action. The concept of growth is notoriously vague and
difficult to define (see Weiss, 1955), but it would probably be generally
agreed that the idea of growth of the whole body, as commonly used,
implies the permanent addition of differentiated tissues but excludes
temporary additions to bulk and weight, such as result from the seasonal
development of the gonads, and also excludes the accumulation of food
J. N. BALL
planted pituitary proved capable of secreting sufficient paralactin to
maintain freshwater survival in Poecilia forrnosa (Ball and Kallman,
1962; Ball et al., 1965), P. latipinna (Ball, 1965b; Ball and Olivereau,
1965), and Xiphophorus ( Schreibman and Kallman, 1964). In P. latipinna
the paralactin from ectopic transplants maintains the normal low rate of
sodium outflux in freshwater and the low rate of sodium turnover in isotonic dilute seawater (Ball, 1968). Although it seems certain that in
cyprinodonts at least, hypothalamic connections are not essential for
secretion of paralactin at normal levels, the absence of rigorously quantitative data on rates of secretion of the hormone in grafted fish compared with normal fish precludes the assumption that a hypothalamic
paralactin-inhibiting factor exists in teleosts, particularly since prolactin
in some birds appear to be under stimulatory hypothalamic control (see
Tixier-Vidal et al., 1966; Meites and Nicoll, 1966).
11. GROWTH HORMONE
A. Introduction
Growth hormone (GH), or somatotropin (STH), is best known and
most readily characterized as the pituitary factor which promotes overall
growth of the body, even when acting in the absence of the other pituitary hormones, for example, when injected into hypophysectomized animals. Many complex actions of the hormone on metabolic processes
underlie this growth promotion, and recent accounts of these metabolic
actions of GH in mammals will be found in the reviews by Knobil and
Hotchkiss ( 1964) and Evans et al. (1966), and in the symposium edited
by Pecile and Miiller (1968). Growth hormone is known from studies in
higher vertebrates to be particularly important as a synergist with other
hormones, including among its properties for instance the power to enhance the effects of tropic pituitary hormones on their target glands
(R. W. Smith et al., 1955; Pickford and Atz, 1957; Evans et al., 1966).
Nearly all studies concerned with the physiology of GH in fishes relate to stimulation of body growth, and there is little published data on
other aspects of its action. The concept of growth is notoriously vague and
difficult to define (see Weiss, 1955), but it would probably be generally
agreed that the idea of growth of the whole body, as commonly used,
implies the permanent addition of differentiated tissues but excludes
temporary additions to bulk and weight, such as result from the seasonal
development of the gonads, and also excludes the accumulation of food