| Abstrakt: |
AbstractThis study investigates whether thyrotropin-releasing hormone (TRH), α-melanocyte-stimulating hormone (α-MSH) and N-acetyl β-endorphin (NAc β-END), or the thyroid hormones thyroxine (T4) and 3,5,3'-triiodothyronine (T3) are involved in the physiological response to temperature changes in the poikilotherm common carp (Cyprinus carpio). Carps were either subjected to a rapid cold exposure or acclimated over time to three different temperatures. Acute cold exposure did not influence blood plasma α-MSH concentrations. Acclimation to 15, 22 or 29°C led to a temperature-dependent increase of both α-MSH and NAc β-END plasma concentrations. Moreover, the in vitro sensitivity to TRH of melanotrope cells (that synthesise these peptides) also correlated positively with ambient temperature. Increased TRH activation stimulated processing of the precursor of α-MSH and NAc β-END, resulting in increased release of both peptides and storage of a surplus of NAc β-END within melanotropes. Plasma T4 levels were highest in carps acclimated to the intermediate temperature tested, and correlated strongly with hypothalamic TRH content. Plasma T3 levels were unaffected by ambient water temperature. We conclude that ambient water temperature influences the sensitivity of melanotrope cells to TRH in carps. This effect, however, is not due to acute temperature change, but evolves during the acclimation process of carps to a new temperature.Copyright © 2003 S. Karger AG, Basel [ABSTRACT FROM AUTHOR] |
