Growth hormone as a function of age and dietary protein: energy ratio in a marine teleost, the gilthead sea bream (Sparus aurata).

We examined in a factorial design the effect of dietary protein (45%, 52% and 60%) and lipids (8%, 12%, 17%) on growth performance and circulating growth hormone (GH) levels of fingerling sea bream (5-month-old) fed to satiation with self-feeders. Daily weight gain (2.6-2.9%) and feed gain ratio (1.1-1.3) of fish fed high protein-low lipid diets were comparable to those found in fast growing strains of rainbow trout. However, increasing hyperphagia in association with the decrease of daily weight gain and feed conversion efficiency were found with the decrease of dietary protein:energy ratio. This growth impairment was linked to increased concentrations of circulating GH, which would exacerbate glucose and lipid intolerance. We consider the elevated concentration of circulating GH to be a risk factor leading to some state of metabolic starvation, in which feeding behavior and feed conversion efficiency are largely altered. From our results, it can be also concluded that circulating and pituitary GH availability decreases progressively from 1- to 3-year-old fish. This blunted GH synthesis and release is discussed in relation to age decrease in the optimum dietary protein:energy ratio.

The use of recombinant gilthead sea bream (Sparus aurata) growth hormone for radioiodination and standard preparation in radioimmunoassay.

A gilthead sea bream growth hormone (sbGH) obtained by cloning and expression of sbGH cDNA was used to develop a sensitive and specific radioimmunoassay (RIA). Iodination of recombinant sbGH (rsbGH) was performed by the classical Chloramine-T method. Specific antiserum, raised in rabbits, was added in a final dilution of 1/36,000. The minimum detectable dose was 30 pg, and the midrange of the assay (ED50) was 275 pg. Intra- and inter-assay coefficients of variation (CV) were 3.3 and 5.8% at ED50 levels. Human GH (hGH), ovine GH (oGH), carp gonadotropin (cGtH), chinook salmon gonadotropin (sGtH), ovine prolactin (oPRL) and recombinant tilapia prolactin (rtiPRL) did not show cross-reactivity. Serial dilutions of chinook salmon GH (sGH) and recombinant rainbow trout GH (rtGH) showed a low but significant cross-reactivity. A good parallelism between rsbGH standard and serial dilutions of native sbGH, plasma and pituitary extracts was observed. In addition, when plasma and pituitary samples were analyzed for GH quantification, non-significant differences were observed within this and previous RIA for native sbGH. Therefore, it appears conclusive that our rsbGH can be used successfully as a standard and radioiodinated hormone in GH assays for gilthead sea bream, which is extensively cultured in the Mediterranean area.

Ration size and protein intake affect circulating growth hormone concentration, hepatic growth hormone binding and plasma insulin-like growth factor-I immunoreactivity in a marine teleost, the gilthead sea bream (Sparus aurata).

The nutritional regulation of the growth hormone liver axis has been studied in gilthead sea bream (Sparus aurata). In a first study, fingerling fish were fed three experimental diets with varying proportions of protein (34, 45 and 55%). A 60% decrease in plasma growth hormone concentration was observed with the increase of specific growth rates and dietary protein levels. An opposite response was observed in hepatic growth hormone-binding sites and plasma insulin-like growth factor-I immunoreactivity that would reflect the insensitivity of liver to growth hormone action during relatively low protein intake. In a second study, fish were fed a commercial diet (55% protein) at different feeding levels (0, 1.2, 2.7 and 5.5 g/(100 g body wt.d). An 84% decrease in plasma growth hormone concentration was observed with the increase of specific growth rates and feeding levels from 0 to 2.7 g/(100 g body wt.d). However, significantly greater growth hormone concentration was found in fish fed 5.5 g/(100 g body wt.d) when compared with fish fed 2.7 g/(100 g body wt.d). Hepatic growth hormone-binding sites and plasma insulin-like growth factor-I immunoreactivity increased with the increase of feeding levels from 0 to 2.7 g/(100 g body wt.d), but these values were lower in fish-fed 5.5 g/(100 g body wt.d) than in those fed 2.7 g/(100 g body wt.d). The physiological importance of these results remains to be clarified, though probably it is a part of the mechanism that diminishes feed utilization for growth at high feeding levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Developmental regulation of growth hormone binding in the gilthead sea bream, Sparus aurata.

The occurrence of growth hormone (GH) binding was investigated in the gilthead sea bream larva, Sparus aurata, using recombinant trout GHII (rtGH) as a tracer. GH binding was detected in all the specimens examined (5, 17, 27 and 40 days after hatching). At 40 days after hatching, we observed a concentration of GH binding in the head region. Specific binding was dependent on protein membrane concentration and Scatchard plots showed a single class of high affinity and low capacity binding sites. Specific binding was inhibited by rtGH and ovine GH in a dose dependent manner. Chinook salmon prolactin and chinook salmon gonadotropin did not compete for 125I-rtGH binding sites. To our knowledge, this is the first report that indicates the presence of specific and saturable GH binding sites during early growth and development of a fish species.

Seasonal changes in circulating growth hormone (GH), hepatic GH-binding and plasma insulin-like growth factor-I immunoreactivity in a marine fish, gilthead sea bream,Sparus aurata.

We have studied the seasonal relationship between growth and circulating growth hormone (GH), hepatic GH-binding and plasma insulin-like growth factor-I immunoreactivity in gilthead sea bream,Sparus aurata. The seasonal increase in plasma GH levels preceded by several weeks the summer increase in growth rates. In contrast, a marked increase in hepatic GH-binding with a high degree of endogenous GH occupancy was found during the period of maximum growth which suggests an enhanced sensitivity of liver to GH action. Thus, circulating levels of immunoreactive IGF-I, probably derived from the liver in response to GH action, were positively correlated with growth throughout the experimental period although a consistent relationship between growth and circulating GH was not found. In spite of this, we consider that, in gilthead sea bream, as in several other teleosts, the availability of endogenous GH can limit growth. Thus, under environmental conditions of suboptimal growth, a single intraperitoneal injection of recombinant rainbow trout GH (rtGH) induced over the dose range tested (0.75, 1.5, 3 µg g BW(-1)) an increase in plasma IGF-I-like immunoreactivity comparable to that seen during the period of maximum growth.