Alan Frank Cook

Ovulatory surge of gonadotropin in the goldfish, Carassius auratus

The periovulatory pattern of circulating gonadotropin is described for the first time in a poikilothermic vertebrate. In sexually mature female goldfish (Carassius auratus) maintained on a 16L:8D photoperiod, ovulation occurs during the latter part of the dark phase, approximately 20 hr after the fish are warmed from 13 to 21°. Serum gonadotropin levels increase gradually during the first half of the light phase, and by the latter part begin to increase rapidly, reaching the peak of the gonadotropin surge by the onset of the dark phase. Gonadotropin levels remain high through the period of ovulation, and decrease markedly by the onset of the following light phase. The findings indicate that the goldfish provides a valuable model for the study of ovulation in teleosts.

Development and validation of a carp growth hormone radioimmunoassay

Purified growth hormone (GH), isolated from pituitary glands of the common carp (Cyprinus carpio), was shown to have biochemical and immunological properties in common with other teleost GH preparations. Intraperitoneal injections of the carp GH, at a dose of 1 microgram/g body wt, resulted in significant increases in body weight in goldfish. In addition, the carp GH was used to prepare an antiserum for the development of a radioimmunoassay (RIA). The displacement curves for serum from goldfish with an intact pituitary gland were parallel to that of the purified cGH in this RIA. In contrast, serial dilutions of serum from hypophysectomized goldfish, and purified goldfish prolactin and carp gonadotropin did not have significant cross reaction. The present study strongly suggests that this RIA is suitable for the measurement of circulating GH levels in the goldfish.

Influence of catecholamines on gonadotropin secretion in goldfish, Carassius auratus.

Serum gonadotropin (GtH) concentrations in female goldfish were measured before and at various times after intraperitoneal injection of drugs altering catecholamine synthesis and neural activities. Reserpine, a depleter of neurotransmitter stores, elevated serum GtH levels compared to controls, suggesting the general involvement of neurotransmitters in altering GtH release. 6-Hydroxydopamine, a catecholaminergic neurotoxin, increased serum GtH concentration, suggesting that catecholaminergic neurons inhibit GtH release. Blocking of L-DOPA and dopamine synthesis by alpha-methyl-para-tyrosine and carbidopa, respectively, but not norepinephrine by diethyldithiocarbamate, raised serum GtH values above those of controls. Injections of an alpha-agonist, clonidine, also increased serum GtH concentrations. These results suggest the existence of an inhibitory dopaminergic and a stimulatory alpha-adrenergic influence on GtH release in goldfish.

The effects of somatostatin on serum growth hormone levels in the goldfish, Carassius auratus

In the present study the effects of somatostatin on serum growth hormone (GH) levels in the goldfish, Carassius auratus, were investigated. A single intraperitoneal injection of either 0.1 or 1.0 micrograms somatostatin/g body wt caused a significant decrease in serum GH levels at 1 h postinjection compared to vehicle-injected controls. Two intraperitoneal injections of somatostatin (1.0 micrograms/g body wt), given 12 hr apart, caused a significant decrease in serum GH levels, compared to both presample and vehicle-injected control groups at 1.5 and 6 hr following the second injection. In fish given two injections of somatostatin, a post inhibitory rebound in serum GH levels occurred by 24 hr following the second injection. Thyrotropin-releasing hormone (1 micrograms/g body wt), given as a control peptide, caused a significant increase in serum GH levels at 24 hr, but no significant changes were found at 1.5 or 6 hr following the second of two intraperitoneal injections given 12 hr apart. The increases in serum GH at 24 hr may be due to stress. The results demonstrate that somatostatin causes a transient decrease in blood GH levels in goldfish.

Periovulatory changes in serum cortisol levels in the goldfish, Carassius auratus.

Sexually mature goldfish maintained under a 16L:8D photoperiod were induced to ovulate by warming from 12 to 21° in the presence of aquatic vegetation. A surge in serum cortisol, measured by radioimmunoassay, occurs at the onset of the dark phase, 4 to 8 hr prior to ovulation. Cortisol may play a physiological role in ovulation in the goldfish.

Influences of Catecholamines on Growth Hormone Release in Female Goldfish, Carassius auratus

The influence of catecholamines on growth hormone (GH) release in female goldfish was investigated by monitoring serum GH levels following injections of drugs known to alter catecholamine synthesis and neural activities. Intraperitoneal (i.p.) injection of 6-hydroxydopamine, a catecholaminergic neurotoxin, or alpha-methyl-p-tyrosine, a catecholamine synthesis inhibitor, decreased serum GH levels. Intraperitoneal injection of L-beta-dihydroxyphenylalanine (L-dopa) increased serum GH concentrations in a dose-dependent manner. The L-dopa-induced increase in serum GH was potentiated by i.p. injection of carbidopa, which would increase the availability of L-dopa to brain tissues by blocking the peripheral conversion of L-dopa to dopamine (DA). These results suggest that L-dopa or one of its catecholamine metabolites acts centrally to increase GH release. Intraventricular (i.v.t.) injection of DA and i.p. injection of apomorphine, a DA agonist that crosses the blood-brain barrier, increased serum GH. Intraperitoneal injection of DA did not alter circulating GH levels in normal fish or fish bearing preoptic lesions that abolish an inhibitory hypothalamic influence on GH release; however, DA increased serum GH in fish which had their blood-brain barrier destroyed by sham operation procedures. These results indicate that DA acts centrally to stimulate GH secretion, possibly by inhibiting the release and/or synthesis of GH release-inhibitory factor. Serum GH concentrations were decreased in a dose-dependent manner by i.p. injection of norepinephrine (NE), whereas i.v.t. injection of NE did not alter serum GH levels. These results indicate that NE acts outside of the blood-brain barrier to decrease serum GH levels in the goldfish, possibly by directly influencing pituitary GH cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Plasma clearance of gonadotropin in goldfish, Carassius auratus, during the annual reproductive cycle

Abstract The present study investigated the plasma clearance of radioiodinated carp glycoprotein gonadotropin (125I-cGtH) in the female goldfish, Carassius auratus, during different phases of the annual reproductive cycle and at two different temperatures. The plasma disappearance of intraarterially injected 125i-cGtH was found to be multiexponential, exhibiting both a rapid and a slow component. Under certain conditions of sexual condition and temperature, the immunoprecipitation of plasma 125I-cGtH provided a significant discrimination between total and trichloroacetic acid-precipitated radioactivity. At 12 ± 1° the plasma metabolic clearance rate (MCR) increased with increasing state of ovarian development. MCR was also increased at 20 ± 1°, relative to 12 ± 1°, in sexually regressed but not in sexually maturing goldfish, suggesting that both temperature and the state of ovarian development may affect the plasma clearance of GtH in goldfish. Plasma GtH levels, as measured by radioimmunoassay, were elevated in both sexually regressed and maturing female goldfish acclimated to 20 ± 1° compared with fish maintained at 12 ± 1°, and at both temperatures plasma GtH levels increased with increasing state of ovarian development. The maximum levels of pituitary GtH were obtained from sexually maturing and mature female goldfish coincident with the highest estimated values of pituitary secretion rate (SR) and the lowest calculated values of plasma initial half-disappearance time. The results of the present study indicate that a number of aspects of the glycoprotein GtH dynamics are markedly different between sexually regressed, and both maturing and mature female goldfish, and that the changes in plasma GtH levels seen during progressive ovarian development are a reflection of progressive increases in the SR of GtH.

Ultrastructural immunocytochemistry of growth hormone cells in the goldfish pituitary gland

The immunocytological activity of an antiserum to carp growth hormone was studied on the goldfish pituitary gland, using a peroxidase-antiperoxidase ultrastructural technique. The reaction was specific for secretory granules in cells in the proximal pars distalis categorized as growth hormone cells on the basis of ultrastructural characteristics. The results support the specificity of the antiserum for growth hormone and provide firm identification of the growth hormone cells in goldfish.

The metabolism of gonadotropin in goldfish, Carassius auratus: tissue uptake and distribution during the reproductive cycle.

The time course of gonadal uptake of intraarterially injected radioiodinated carp glycoprotein gonadotropin (125I-cGtH) was determined in goldfish maintained at 12 ± 1 or 20 ± 1°, during different stages of the annual reproductive cycle. The results indicated that elevated temperature could alter the pattern of uptake in goldfish undergoing ovarian recrudescence but not in sexually regressed female goldfish. Also when changes in the ovarian surface area to volume ratio are accounted for, the amount of 125I-cGtH incorporated into the ovary on a per-unit-weight basis, is much greater in sexually maturing and mature female goldfish compared to sexually regressed fish. The tissue distribution of trichloroacetic acid-precipitated 125I-cGtH determined in sexually regressed male and female goldfish; 15 min after injection, indicated that the kidney provided the greatest concentration of tissue-specific activity. In contrast, the gonads of sexually regressed goldfish accumulated a relatively small amount of 125I-cGtH in terms of both tissue-specific activity and whole-organ accumulation. The possible roles of the gonad in ovarian recrudescence are discussed in relation to recent information concerning both the pituitary gland secretion and plasma metabolic clearance rate of gonadotropin.

Effects of hypothalamic lesions on serum growth hormone levels and growth rates in goldfish, Carassius auratus

Serum growth hormone (GH) levels and growth rates of goldfish were measured concurrently following discrete electrothermic lesions of a number of hypothalamic nuclei. Following lesions of the nucleus preopticus periventricularis (NPP), significant increases in serum GH levels were evident at 4 weeks postlesioning in comparison to both sham-operated and normal control groups. In addition, the NPP-lesioned fish showed significant increases in both total body weight and standard length increments compared to control groups. Lesions in other hypothalamic areas including the nucleus anterior tuberis, nucleus lateralis tuberis and the nucleus recessus lateralis had no consistent effect on growth rates or serum GH levels. The present results suggest that the NPP is concerned with the inhibition of GH secretory function in the goldfish.