Ontogeny of vasoconstrictor neurohypophysial hormone function in rats

Abstract

This in vitro study examined the ontogeny of arginine vasopressin (AVP) and arginine vasotocin (AVT) compared with norepinephrine (NE)-mediated contraction in rat thoracic aortas. Aortas from three age groups (2-3 days, 6-7 days, and 12 wk) of Sprague-Dawley rats were used. Ring segment resting length was adjusted to optimize tension developed to a dose that produces half-maximal tension of NE in Krebs solution (pH 7.4, 37 degrees C) and gassed with 95% O2-5% CO2. Cumulative dose-response curves were generated for KCl (5-100 mM), NE (10(-10)-10(-5) M), AVP, and AVT (both 10(-10)-10(-6) M) in the presence and absence of a selective V1 vasopressinergic inhibitor, [1-(beta-mercapto-beta,beta-cyclopentamethylenepropionic acid), 2-(O-methyl)tyrosine]arginine vasopressin ([d(CH2)5Tyr(Me)]AVP). A progressive increase in sensitivity among all age groups was found for KCl and NE. There was a slight decrease in sensitivity to both AVP and AVT in the 1st wk. Maximum contractile response to NE increased between 2-3 and 6-7 days, whereas no change was observed for KCl, AVP, or AVT. AVP- and AVT-mediated contractions were selectively inhibited by [d(CH2)5Tyr(Me)]-AVP. These results suggest 1) receptor-mediated contractility is present from 2 days of age for NE, AVP, and AVT; 2) sensitivity to KCl and NE increases progressively during postnatal development, whereas sensitivity to AVP and AVT slightly decreases in the 1st wk with no progressive age-related increase by 12 wk; 3) AVP and AVT mediate contraction via a similar V1-like receptor.

Differential Ontogeny of in Vitro Vascular Responses to Three Categories of Calcium Channel Antagonists in Rats

“…Shown in Table 1 are the control equilibrium contractions with the doses of KC1 and NE used. For all ages, both isotonic KC1 concentrations (2-3 d, 50 mM; 1 wk, 40 mM; 12 wk, 20-25 mM) and NE concentration (0.03 pM) approximated the ED50 values obtained in our previous study (8).…”

“…Present results demonstrate an increase in sensitivity to two categories of calcium channel antagonists during the same time period in rats when contractile responses to KC1 and NE are rapidly developing (8). In contrast, results employing a third category of calcium channel antagonists, represented by nifedipine, indicate a different ontogeny than simply a generalized increase in calcium channel antagonists function, inasmuch as nifedipine was equally effective at 2-3 d through 12 wk.…”

“…Aortas were suspended in an organ bath with 25 mL of Krebs' solution (37°C; pH 7.4), gassed with 95% 0~5 % C02, and equilibrated for 60 min with a bath change every 15 min. Vessels were stretched to the optimal point on their length tension curve determined by equilibrium tension developed to a EDSo of NE (8,9). Optimal passive forces were: 2-3 d, 0.32 k 0.01 g; 1 wk, 0.38 f 0.01 g; and 12 wk, 3.2 f 0.03 g. Endothelial function was assessed by observing relaxation upon addition of 10 pM acetylcholine to rings preconstricted with a ED,, of NE.…”

“…We have previously (8) demonstrated the ontogeny of the concentration-dependent response in thoracic aortic rings among 2-d-, 1-wk-, and 1 Zwk-old rats for both potential-mediated (KClinduced) and receptor-mediated (NE-induced) contraction. Thus, calcium channel function is present from 2 d of age with perhaps increasing physiologic function during development.…”

Rat pulmonary arterial smooth muscle myosin light chain kinase and phosphatase activities decrease with age

“…We have previously shown that the pulmonary and systemic vascular smooth muscle of the newborn sheep has a lesser potential for force development, and a longer relaxation half-time compared with the adult (6,9). Similar agerelated systemic vascular smooth muscle differences have been reported in relation to its maximum contraction in the rabbit (27) and rat (22), as well as to the degree of nitric oxideinduced relaxation in the guinea pig (5).…”