Fish Physiology and Biochemistry 22: 125–133, 2000. © 2000 Kluwer Academic Publishers. Printed in the Netherlands. 125 Effect of a prolactin pharmacological stimulant (sulpiride) and suppressant (bromocriptine) on heat shock protein 70 expression in silver sea bream, Sparus sarba E.E. Deane, S.P. Kelly,I.N.K. Chow and N.Y.S. Woo * Department of Biology, The Chinese University of Hong Kong, Shatin, N. T., Hong Kong SAR, China (Phone: (852) 26096148; Fax: (852) 26035646; E-mail: normanwoo@cuhk.edu.hk); * Author for correspondence Accepted: August 5, 1999 Key words: hormone, HSP70, mRNA expression, protein expression, seabream, teleost fish Abstract Heat shock protein 70 (HSP70) expression was assessed in hepatic tissue of silver sea bream, Sparus sarba. Using a combination of reverse transcription and PCR we have cloned a 794 base pair HSP70 cDNA fragment. This clone hybridized to a 2.3kb HSP70 mRNA transcript which was elevated 2.5 fold after acute heat shock exposure. Cold shock however, had no effect on HSP70 expression. In order to study the effect of prolactin on silver sea bream hepatic HSP70, groups of fish received either ovine prolactin (oPRL), sulpiride or bromocriptine, daily, over a seven day period. Treatment with oPRL and sulpiride resulted in a reduction in the relative abundance of hepatic HSP70 mRNA by 48 and 52%, respectively. Also hepatic HSP70 levels were reduced by 69 and 46% (as determined by immunoblotting) after oPRL and sulpiride administration, respectively. The administration of bromocriptine significantly increased both HSP70 mRNA and protein levels by 197 and 240%, respectively. The data from this study provides strong support for the importance of prolactin in regulating HSP70 expression in silver sea bream. Introduction The heat shock protein (HSP) family, are a group of proteins that have been identified in an array of evolu- tionary diverse organisms which are classified accord- ing to their molecular size as determined by denaturing protein gel electrophoresis (Morimoto et al. 1994). Of this important group of proteins it is the 70 kDa heat shock protein (HSP70) which has been most widely studied and its amino acid sequence has been shown to be highly homologous among many organisms such as soybean (Roberts and Key 1991), zebra fish, Danio rerio (Graser et al. 1996), chicken (Morimoto et al. 1986) and human (Roux et al. 1994). Many studies have clearly demonstrated that thermal shock induces fish HSP expression either in vitro (Mosser and Bols 1988; Airaksinen et al. 1998) or in vivo (Dyer et al. 1991; Koban et al. 1991; Dietz and Somero 1992). Furthermore, exposure to hypoxia (Airaksinen et al. 1998), heavy metals (Heikkila et al. 1982; Misra et al. 1989) and infectious agents (Cho et al. 1997) have all been demonstrated to induce fish HSP expression in vitro. Classical stress hormones such as cortisol are known to be rapidly released into the circulation of stressed fish (Wendelaar Bonga 1997), but it is not clear whether this hormone is related in any way to the regulation of piscine HSP expression. Vijayan et al. (1997) demonstrated that hepatic HSP70 lev- els remained unchanged during handling stress even though the concentration of circulating cortisol was elevated. Under some situations, prolactin (PRL) and growth hormone have also been implicated to be in- volved in the stress response in several fish species (Auperin et al. 1997) including silver sea bream, (Nar- naware et al. 1998; Kelly et al. 1999). Presently, the importance of hormonal regulation of piscine HSP expression has only been reported in a single study (Deane et al. 1999) and as yet the significance of hor-