Administration of arginine does not alter material circulating concentration of C-type natriuretic peptide in pregnant sheep: A thesis submitted in partial fulfilment of the requirements for the Degree of Bachelor of Science with Honours

C-type natriuretic peptide (CNP) circulates at higher levels in the circulation of ewes pregnant with multiple fetuses than in those with singletons. Because parenteral administration of arginine can mitigate the nutritional constraint that occurs in multi-fetal pregnancies, it was hypothesised that treatment with arginine would decrease plasma CNP concentration in ewes pregnant with triplets, but have no effect on singleton pregnancies. To test this, pregnant ewes carrying singles or triplets (about day 100 of gestation) received an i.v. bolus injection of either saline solution (control, n = 6) or arginine solution (treatment, n = 6), 3 times a day for a period of 3 days. Blood samples were collected and maternal plasma CNP and NTproCNP concentrations were measured. The mean maternal plasma concentration of CNP and NTproCNP was significantly higher in triplet pregnancies than singleton pregnancies, regardless of treatment (CNP, P < 0.001; NTproCNP P < 0.001). However, there was no effect of the arginine treatment on maternal circulating concentrations of CNP and NTproCNP in ewes pregnant with single or triplet fetuses (P = 0.784). The mean ratio of NTproCNP to CNP concentration in maternal plasma in the singleton pregnancies was double that of the triplet pregnancies (9.2 ± 0.73, 4.8 ± 0.51 , mean± SEM, respectively, P < 0.001). On the basis of these findings the hypothesis under test was rejected, thus it is concluded that the variation in maternal CNP concentration is not a result of fetal/placental signalling of nutritional constraint