Katherine Drennon | PubMed Health

PubMed2004

Salinity acclimation affects the somatotropic axis in rainbow trout.

In this study, we set out to examine the role of the somatotropic axis in the ion-regulation process in rainbow trout. Specifically, our objective was to examine whether plasma insulin-like growth factor-binding proteins (IGFBPs) are modulated by gradual salinity exposure. To this end, freshwater (FW)-adapted rainbow trout were subjected to gradual salinity increases, up to 66% seawater, over a period of 5 days. During this acclimation process, minimal elevations in plasma Ca2+ and Cl- were seen in the salinity-acclimated groups compared with FW controls. There were no changes in plasma Na+ levels, and only a minor transient change in plasma cortisol levels was seen with salinity exposure. The salinity challenged animals responded with elevations in plasma growth hormone (GH) and IGF-I levels and gill Na+-K+-ATPase activity. We identified IGFBPs of 21, 32, 42, and 50 kDa in size in the plasma of these animals, and they were consistently higher with salinity. Despite the overall increase in IGFBPs with salinity, transient changes in individual BPs over the 5-day period were noted in the FW and salinity-exposed fish. Specifically, the transient changes in plasma levels of the 21-, 42-, and 50-kDa IGFBPs were different between the FW and salinity groups, while the 32-kDa IGFBP showed a similar trend (increases with sampling time) in both groups. Considered together, the elevated plasma IGFBPs suggest a key role for these binding proteins in the regulation of IGF-I during salinity acclimation in salmonids.

Acclimatization↗

PubMed2003

Development of an enzyme-linked immunosorbent assay for the measurement of plasma growth hormone (GH) levels in channel catfish (Ictalurus punctatus): assessment of environmental salinity and GH secretogogues on plasma GH levels.

We report the development of a sensitive, and specific, competitive, antigen-capture enzyme-linked immunosorbent assay for the measurement of channel catfish (Ictalurus punctatus) growth hormone (cfGH). The detection limit of the assay (90% binding) was 2.0ng/ml and the ED(50) value (standard curve range 150-0.59 ng/ml) was 67.3 ng/ml. Recovery of cfGH-spiked plasma samples was determined to be 102%. Dose-response inhibition curves using serially diluted pituitary homogenates and plasma samples consistently showed parallelism with the standard curves using purified cfGH. The GH antibody (rabbit anti-catfish GH) specificity was demonstrated in competitive binding curves employing heterologous hormones and purified channel catfish prolactin (cfPRL). These studies show that there was no significant (0.006%) binding of cfPRL (competitive inhibition of cfGH binding), or heterologous hormones, within the working range of the assay. To physiologically validate the assay, catfish were injected (100 microg/g body weight, 3 injections every 5 days) with either bovine GHRH(1-29)-amide or the synthetic hexapeptide GHRP-2 (KP-102: D-Ala-D-beta-Nal-Ala-Trp-D-Phe-Lys-NH(2)) suspended in corn oil. Following the last injection, half of the animals were sampled for plasma and the remaining transferred from fresh water (FW) to 12 ppt seawater (BW: brackish water). Twenty-four hours after transfer to BW, animals were again sampled for plasma. Plasma GH levels were significantly (p<0.001) elevated in all the BW groups (control, KP-102, and bGHRH), compared with the FW (fresh water) groups. In addition, plasma GH levels were significantly (p<0.001) elevated by treatment with either of the GH secretogogues, KP-102 or bGHRH. Our findings demonstrate that two regulatory mechanisms of GH elevation, one which is seen in euryhaline teleosts (salinity-induced GH levels) and another, which has been recently described in teleosts (GHRP-induced GH levels), are present in the stenohaline channel catfish.

Animals↗