Abstract
The objectives of this study were to investigate and compare the responses of atrial natriuretic peptide (ANP) and B-type natriuretic peptide (BNP) in the circulation of hydrated, dehydrated, and dehydrated losartan - treated camels; and to document the cardiac storage form of B-type natriuretic peptide in the camel heart. Eighteen male camels were used in the study: control or hydrated camels (n = 6), dehydrated camels (n = 6) and dehydrated losartan-treated camels (n = 6) which were dehydrated and received the angiotensin II (Ang II) AT-1 receptor blocker, losartan, at a dose of 5 mg/kg body weight intravenously for 20 days. Control animals were supplied with feed and water ad-libitum while both dehydrated and dehydrated-losartan treated groups were supplied with feed ad-libitum but no water for 20 days. Compared with time-matched controls, dehydrated camels exhibited a significant decrease in plasma levels of both ANP and BNP. Losartan-treated camels also exhibited a significant decline in ANP and BNP levels across 20 days of dehydration but the changes were not different from those seen with dehydration alone. Size exclusion high performance liquid chromatography of extracts of camel heart indicated that proB-type natriuretic peptide is the storage form of the peptide.We conclude first, that dehydration in the camel induces vigorous decrements in circulating levels of ANP and BNP; second, blockade of the renin-angiotensin system has little or no modulatory effect on the ANP and BNP responses to dehydration; third, proB-type natriuretic peptide is the storage form of this hormone in the heart of the one-humped camel.
Highlights
The one-humped camel (Camelus dromedarius), widely distributed in the Gulf countries, is well able to survive water deprivation for long periods without ill effects
This study was planned on the basis of three underlying hypotheses: first, that dehydration would induce a decline in plasma levels of atrial natriuretic peptide (ANP) and B-type natriuretic peptide (BNP); second, that blockade of ANG II type 1 receptors would enhance the fall in ANP and BNP levels; and third, that the dominant form of BNP in the camel heart would be in a large molecular weight form consistent with proBNP
Size exclusion HPLC of extracts from camel atrial tissue demonstrated a single immunoreactive peak in fractions 24–26 (Figure 2) which eluted one fraction later than recombinant human proBNP standard but well ahead of synthetic human NTproBNP and BNP1–32 standards. This indicates that immunoreactive BNP in the camel heart is in the form of proBNP with an approximate molecular weight of 11,600 Da, and close to the theoretical molecular weight of camel proBNP (11,734 Da) calculated from the dromedary sequence provided by Osman et al and in Genebank:BAD21300.1 [8]
Summary
The one-humped camel (Camelus dromedarius), widely distributed in the Gulf countries, is well able to survive water deprivation for long periods without ill effects. Whereas the effects of dehydration on some of these hormones are well documented in certain species, this is not so for the camel where responses in circulating levels of the cardiac natriuretic peptides in particular are unknown. This is somewhat surprising given that these peptides are known to have actions which serve to maintain sodium and water balance and, in particular, to prevent circulatory overload through potent effects on the kidney (natriuresis and diuresis), the central nervous system (inhibition of thirst, salt appetite and antidiuretic hormone secretion) and the adrenal gland (inhibition of aldosterone secretion) [2]. This study was planned on the basis of three underlying hypotheses: first, that dehydration would induce a decline in plasma levels of ANP and BNP; second, that blockade of ANG II type 1 receptors would enhance the fall in ANP and BNP levels; and third, that the dominant form of BNP in the camel heart would be in a large molecular weight form consistent with proBNP
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