Recurrent hypoxic exposure and reflex responses during development in the piglet.

The effects of recurrent hypoxia on cardiorespiratory reflexes were characterized in anesthetized piglets at 2-10 d (n=15), 2-3 weeks (n=11) and 8-10 weeks (n=8). Responses of phrenic and hypoglossal electroneurograms (ENG(phr) and ENG (hyp)) to hypoxia (8% 0(2), bal N(2), 5 min), hypercapnia (7% CO(2) bal O(2), 5 min) and intravenous capsaicin were tested before and after recurrent exposure to 11 episodes of hypoxia (8% O(2) bal N(2), 5 min). In piglets 2-10 d, ENG(phr) response to hypoxia declined in proportion to the number of hypoxic exposures; however, ENG (hyp) response to hypoxia was unchanged.

Carotid bodies and ventilatory response to hypoxia in aminophylline-treated piglets.

Peripheral chemoreceptors may be immature in neonatal animals, exhibiting maturational changes in the perinatal period. Even though methylxanthines are respiratory stimulants, many premature neonates do not respond to them. Thus, we hypothesized that carotid body activity is necessary for aminophylline to reverse hypoxia-induced respiratory depression.

Central effects of endothelin on respiratory output during development.

Both endothelin-1 protein and endothelin-1 specific binding sites have been identified in areas of the medulla oblongata involved in respiratory control. We examined whether endothelin acting centrally affects respiratory output during early postnatal life. We initially examined the effect of intracisternally administrated endothelin on respiratory output in 10 2- to 18-day-old piglets.

Regulation of expiratory muscles during postnatal development in anesthetized piglets.

We compared maturation of the responses of the rib cage [triangularis sterni (TS)] and abdominal [transversus abdominis (TA)] expiratory muscles with each other and with the responses of the diaphragm (DIA) during hypercarbic and hypoxic stimulation. Studies were performed in anesthetized (urethan and chloralose) piglets of two age groups (< 6 days, n = 10; 14-21 days, n = 11) before and after bilateral cervical vagotomy. Hypercarbia (7% CO2-93% O2) was associated with comparable sustained increases in the minute electromyograms (EMGs) of both TS and TA, which were closely coupled to the DIA responses in both age groups.

Development of cholinergic innervation and muscarinic receptor subtypes in piglet trachea.

We studied physiological and pharmacological maturation of cholinergic innervation to tracheal smooth muscle in piglets at three ages: < 7 days, 2-3 wk, and 10 wk. Change in tracheal tension was measured in vivo from a tracheal segment and normalized for its size. Electrical vagal stimulation induced a significantly weaker increase in tracheal tension at < 7 days when compared with 2-3 and 10 wk.