A critical appraisal of two common "neonatal" experiment subjects

Necrotizing enterocolitis in a neonatal piglet model

The aim of this study was to develop an animal model for necrotizing enterocolitis (NEC). Twenty-five neonatal Hanford minipigs had carotid artery and external jugular vein catheters and rectal Clinical Tonomitors placed under anesthesia. Experimental animals were subjected to a hypoxic insult (50% reduction in baseline PaO2 for 30 minutes) and hypothermic stress (core temperature reduced to 35 degrees C for 30 minutes). Regular oral diet was resumed and the survivors were euthanized 3 to 4 days later. All animals underwent necropsy with gross and histopathological evaluation of the entire bowel. Of 22 experimental animals, 14 survived (64%) and 8 (36%) died of pulmonary hemorrhage. Of the 14 survivors, 8 (57%) had gross and microscopic evidence of NEC. Six of the total 25 animals (24%) sustained rectal perforations from the tonometer. Of 3 control animals, one died of pulmonary hemorrhage and the two survivors had normal intestine. This model successfully produced gross and histological evidence of NEC. The tonometer shows promise as a predictor of NEC provided technical modifications can reduce the complication rate.

Maturation of circulatory system in three mammalian models of human development

The review surveys the literature on maturation of vasoconstrictor and vasodilator functions in cerebral, renal and intestinal circulations of three non-primate models of human development. An ovine model has been refined for use at both fetal and neonatal stages of development. Important variables controlling regional circulations in the lamb fetus at term include arterial O2 content and pCO2 (brain), angiotensin-II (kidney) and norepinephrine (small intestine). Blood flow autoregulation to decreasing perfusion pressure has been inferred for the renal circulation of the neonate. A canine model has been employed in the postnatal period, usually later than the first week after birth. Important variables controlling regional circulations in the young puppy include arterial pO2 and pCO2 (brain) and epinephrine and angiotensin-II (kidney). Blood flow autoregulation to decreasing pressure has been demonstrated in the cerebral circulation at birth and in the renal circulation at one week thereafter. The intestinal circulation has not been studied with respect to blood flow control. A porcine model has been examined from birth through at least two months of postnatal life. Important variables controlling regional circulations in swine at birth include adrenergic nerve stimulation, arterial pCO2 (brain), angiotensin-II (kidney) and norepinephrine (kidney and small intestine). Blood flow autoregulation to decreasing perfusion pressure has been demonstrated in the brain by the fourth day, in the kidney by the end of the second week and in the small intestine by the end of the first month after birth. The advantage of each model for further investigation of functional maturation of regional circulatory control is summarized.

Effect of age on epinephrine-induced arrhythmias during halothane anaesthesia in pigs

The effect of age on the arrhythmogenicity of epinephrine during halothane anaesthesia was studied in pigs of two different age groups. At a stable alveolar concentration of 0.84 volumes per cent halothane, ventricular arrhythmias could not be elicited in one- to three-day-old pigs by a 100 micrograms X kg-1 infusion of epinephrine. PVCs were produced in 50- to 55-day-old pigs at a mean epinephrine dose of 9.55 micrograms X kg-1. Heart rate, systolic blood pressure, and rate-pressure product were significantly higher before and during the epinephrine infusion in the 50- to 55-day-old pigs. It is concluded that there is an age dependent effect upon epinephrine induced arrhythmias during halothane anaesthesia in pigs.

Age-related cardiovascular effects of catecholamines in anesthetized piglets

We studied cardiac and peripheral circulatory effects of graded doses of catecholamines (0.05-1.0 microgram/kg) in piglets aged less than or equal to 1 day, 2--4 days, 1 wweek, 2 weeks, and 2.5-3 months, under anesthesia with pentobarbital. We evaluated cardiovascular function from simultaneous recordings of aortic pressure, ventricular pressure and its first derivative, heart rate, and phasic carotid and femoral blood flows. We calculated vascular resistance as the ratio of mean aortic pressure to mean flow. The age of onset of a given cardiovascular response was determined, and magnitudes of each type of response were compared among the age groups. Norepinephrine elevated the blood pressure at all doses in piglets of all ages, elicited reflex bradycardia only in older piglets, and increased carotid resistance. Epinephrine elevated the blood pressure at all doses in piglets less than 1 week old, but low doses lowered the blood pressure in piglets older than 1 week of age; resistance changes in the femoral and carotid circulations were variable except in the 2.5-3 month age group. Isoproterenol increased cardiac contractility at all doses in piglets of all ages and increased heart rate at low doses in piglets older than 2 days of age; however, blood pressure and femoral resistance decreases were age and dose dependent. There were age-related differences in the catecholamine dose required to elicit a given cardiac or peripheral circulatory effect and age-related differences in the direction and magnitude of such effects. These results provide evidence for differing rates of postnatal maturation of cardiovascular alpha- and beta- adrenergic mechanisms in swine.