Search

Development of vasomotor responses in fetal mesenteric arteries. Am J Physiol Heart Circ Physiol 279: H1097-H1105, 2000.--Changes in mesenteric arterial diameters were studied using intravital microscopy in chick fetuses at days 13 and 17 of incubation, corresponding to 0.6 and 0.8 fetal incubation time, both during 5 min of hypoxia followed by 5 min of reoxygenation and after topical administration of increasing concentrations, ([10.sup.-6]-[10.sup.-2] M) of norepinephrine (NE) and acetylcholine (ACh). Baseline diameters of second-order mesenteric arteries increased from 56 [micro]m at 0.6 incubation to 75 [micro]m at 0.8 incubation. Acute hypoxia induced a reduction in arterial diameter to 87 [+ or -] 4.4% of baseline at 0.6 incubation and to 44 [+ or -] 6.7% at 0.8 incubation (P [is less than] 0.01). During reoxygenation, mesenteric arteries dilated to 118 [is less than] 6.5% and 121 [is less than] 7.5% of baseline at 0.6 and 0.8 fetal incubation time, respectively. Phentolamine did not affect the vasoconstriction during hypoxia at 0.6 incubation, whereas this [Alpha]-adrenergic antagonist significantly attenuated the vasoconstrictor response at 0.8 incubation (to 93 [+ or -] 2.7% of baseline, P [is less than] 0.01). Topical NE induced maximal vasoconstriction to 71 [+ or -] 3% of baseline at 0.6 incubation and to 35 [+ or -] 3.8% at 0.8 incubation (P [is less than] 0.01). Maximal vasodilation to topical ACh was 113 [+ or -] 4.4% and 122 [+ or -] 4.8% of baseline at 0.6 and 0.8 incubation, respectively. These in vivo findings show that fetal mesenteric arteries constrict in response to acute hypoxia and that the increase in magnitude of this vasoconstrictor response from 0.6 to 0.8 of fetal development results from an increase in adrenergic constrictor capacity. cardiovascular development; hypoxia; necrotizing enterocolitis; norepinephrine; acetylcholine

Intracellular free Ca2+ concentration ([Ca2+]i) plays an essential role in physiological regulatory processes and common pathological conditions. Better understanding of these phenomena is still hampered by problems encountered in the quantitative assessment of [Ca2+]i changes, especially in blood-perfused organs. This study demonstrates that the ratiometric fluorescence technique can be adapted for quantitative in vivo [Ca2+]i determinations. The rat spinotrapezius muscle was topically loaded with indo 1-AM and imaged by a cooled digital camera. Ratio images were calculated in small regions (100 micrometers x 100 micrometers) practically devoid of large vessels in the resting state, after 30 min of ischemia, 20 min of reperfusion, or ionomycin or manganate treatments. When we assumed an average [Ca2+]i of 100 nM in the resting blood-perfused muscle, ischemia increased [Ca2+]i to approximately 200 nM. During reperfusion [Ca2+]i decreased to approximately 140 nM. Ionomycin induced an increase in [Ca2+]i to well above 750 nM. Manganate reduced Ca2+-dependent fluorescence to virtually zero. Our main conclusion is that changes in [Ca2+]i can be monitored and quantitatively determined in vivo.

Angiotensin II acts as a growth factor in the cardiovascular system and has been implicated in angiogenesis. The existence of at least two types of angiotensin II receptors, the AT1 and the AT2 receptors, has been suggested by ligand binding studies. We used three different AT receptor antagonists to study the receptor mediating angiotensin II-induced angiogenesis in the chorioallantoic membrane (CAM) of the chick embryo. Angiotensin II caused pronounced angiogenesis of pre- and postcapillary vessels of 30-40%. This response could only be blocked by adding the peptidergic AT2 antagonist CGP-42112A. The nonpeptidergic AT2 antagonist PD123319 and AT1 antagonist losartan (DuP 753) were not effective. In addition, we used radioligand binding studies with a range of ligands to define the nature of the receptor. Our results show a high density of specific single class AT receptor with a total number of binding sites of 1,190 fmol/mg protein and an affinity constant for angiotensin II of 2.7 nM. The inhibitory concentrations (IC50) for CGP-42112A, PD 123319 and losartan were 724, > 100,000, and 59,000 nM, respectively. Our studies suggest that these binding sites act as receptors for angiotensin II-induced angiogenesis. Both functional and radioligand binding studies suggest that the receptor is different from the classical mammalian AT1 and AT2 receptors.