Temperature has a major influence on cardiac natriuretic peptide in salmon.

1. Natriuretic peptides have a major role in fluid and electrolyte homeostasis in vertebrates. Ambient temperature has a major influence on physiological processes in ectothermic animals. Here we have studied the mechanisms of regulation of a natriuretic peptide, sCP (salmon cardiac peptide), in salmon (Salmo salar) acclimatised and acclimated to varying temperatures. 2. The circulating and cardiac levels of sCP were found to be markedly upregulated in warm-acclimatised and warm-acclimated salmon. The release of sCP from isolated in vitro perfused salmon ventricle was, however, not increased by acclimation to higher temperatures, either in basal conditions or when stimulated by mechanical load. 3. Concomitant measurements of circulating sCP and the biologically inert N-terminal fragment of pro-sCP showed that the upregulation of circulating sCP at warm ambient temperature results from decreased elimination rather than increased secretion of sCP. This is the first direct evidence that changes in the elimination of a natriuretic peptide are used for important physiological regulation. 4. We found a paradoxical increase in cardiac sCP mRNA levels at cold temperatures which coincided with hypertrophy of the heart. sCP gene expression may therefore serve as a marker of cardiac hypertrophy in salmon, in analogy to that of atrial and brain natriuretic peptide (ANP and BNP, respectively) in mammals. 5. These results show that temperature has a major influence on the regulation of natriuretic peptide production and clearance in salmon. Salmon CP offers a novel model for the study of the endocrine function of the heart.

Effects of seasonal photoperiod on serum 25-hydroxycholecalciferol and calcium in reindeer, Rangifer tarandus tarandus.

In order to understand the effects of solar irradiance on calcium metabolism we measured serum 25-hydroxycholecalciferol and total calcium levels monthly in 6 female nonpregnant reindeer maintained in the Oulu area (65 degrees N). Mean monthly serum total calcium levels varied slightly and the highest levels were seen in October. Serum 25-hydroxycholecalciferol levels were highest in October but the monthly variation was also slight. The small monthly variation of the analytes' abundance and the fact that they peaked not until 4 months after the longest day, (i.e. the main stimulus for vitamin D synthesis) could have something to do with the supplementation of this vitamin in the diet of the captive reindeer.

Novel salmon cardiac peptide hormone is released from the ventricle by regulated secretory pathway.

We used the secretion of the novel salmon cardiac peptide (sCP) as a model to examine the mechanisms of ventricular hormone release. Mechanical load increased dose dependently the secretion of immunoreactive sCP from isolated perfused salmon ventricle, with 3. 3-fold increase when a load of 13 cmH(2)O was applied. Endothelin-1 (5 nmol/l) was also able to rapidly increase the secretion of sCP. The released peptide corresponded to the biologically active sCP-29, whereas the large ventricular storage consisted of pro-sCP-sized material. With the use of immunoelectron microscopy, a large number of granules containing immunoreactive sCP could be detected in salmon ventricle. As judged by RNA blot analysis, there was very active basal expression of the sCP gene in the ventricle, which was not increased by mechanical load of up to 2-h duration. Our results show that the ventricle actively expresses the gene of sCP, stores the prohormone in secretory granules, and releases the peptide in response to mechanical load and endothelin-1. Thus the salmon ventricle uses the regulated pathway to produce and release a hormone structurally related to the mammalian natriuretic peptides.

Annual serum PICP and ICTP and antler growth in female reindeer (Rangifer tarandus tarandus).

Annual cycle of type I collagen formation and degradation and antler growth was studied in six adult female reindeer, Rangifer tarandus tarandus. Blood samples were collected twice a week during 1 year. Antler length was measured weekly during the antler growth period. An assay for human PICP, the carboxyterminal propeptide of type I procollagen, was used as an indicator of type I collagen formation and an assay for bovine ICTP, the carboxyterminal telopeptide of type I collagen, as an indicator of type I collagen degradation. PICP was clearly increased during the antler growth period. Also ICTP was slightly elevated during antler growth, but the highest values were found in autumn and winter. Our statistical analysis revealed that changes in lagged values (from 3 to 6 weeks) of PICP could be linked to the subsequent changes in the growth rate of the antler, although the highest values of PICP were found during the final third of antler growth. ICTP had significant predictive power as well, but the connection with the growth rate seemed more immediate than that of PICP. In conclusion, antler collagen synthesis can be predicted by PICP, but also ICTP was related to the antler growth.