Maturation of the angiotensin II cardiovascular response in the embryonic White Leghorn chicken (Gallus gallus)

Abstract

Angiotensin II (Ang II) is an important regulator of cardiovascular function in adult vertebrates. Although its role in regulating the adult system has been extensively investigated, the cardiovascular response to Ang II in embryonic vertebrates is relatively unknown. We investigated the potential of Ang II as a regulator of cardiovascular function in embryonic chickens, which lack central nervous system control of cardiovascular function throughout the majority of incubation. The cardiovascular response to Ang II in embryonic chickens was investigated over the final 50% of their development. Ang II produced a dose-dependent increase in arterial pressure on each day of development studied, and the response increased in intensity as development progressed. The Ang II type-1 receptor nonspecific competitive peptide antagonist [Sar(1) ile(8)] Ang II blocked the cardiovascular response to subsequent injections of Ang II on day 21 only. The embryonic pressure response to Ang II (hypertension only) differed from that of adult chickens, in which initial hypotension is followed by hypertension. The constant level of gene expression for the Ang II receptor, in conjunction with an increasing pressure response to the peptide, suggests that two Ang II receptor subtypes are present during chicken development. Collectively, the data indicate that Ang II plays an important role in the cardiovascular development of chickens; however, its role in maintaining basal function requires further study.

Fig. 1

Representative traces from two different 21-day-old embryonic chickens. These traces illustrate the arterial pressure (P _A) and heart rate (f _H) response to an injection of a Ang II (1,000 ng/kg) alone, and b after pretreatment with [Sar¹ ile⁸] Ang II (4,000 ng/kg). For each trace, the arrow indicates the point of Ang II (1,000 ng/kg) injection. The bracket indicates a period of 5 min

Fig. 2

The change in P _mean (a) and f _H (b) in response to increasing concentrations of Ang II injected into embryonic chickens on day 13(filled diamonds), 17 (filled triangle), 19 (open square), 20 (open triangle), and 21 (filled circle). Different letters between the incubation age groups represent significant differences in the degree of change in response to each dose. Responses that were similar are bracketed. A single dollar symbol signifies that the day-21 response did not differ from that of days 13 and 17. Double dollar symbol signifies that the response on day 20 did not differ from that of day 13. An asterisk indicates a significant reduction in f _H following an injection of Ang II on days 19 and 21 only. The data are presented as mean ± SE. The P _mean response was significant on all days of development except for the lowest dose, on day 19. See Table 2

Fig. 3

The peak change in P _mean following an injection of Ang II 1,000 ng/kg when given as a single injection (open bar), or in a separate group following pre-injection with [Sar¹ ile⁸] Ang II 4,000 ng/kg (filled bar). An asterisk indicates a significant (p < 0.05) difference in the pressure response between the two injections on a given day of incubation. The data are presented as mean ± SE

Fig. 4

The control plasma Ang II concentrations in embryonic chickens during the period of development studied. Different letters between any two incubation age groups indicates a significant (p < 0.05) difference in the plasma Ang II concentration between the groups. The data are presented as mean ± SE

Fig. 5

The Ang II mRNA concentration per 5 ng of total RNA in a whole CAMs, and b hearts from embryonic chickens at 13, 17, 19, and 20 days of development. The data are presented as mean ± SE