Altered inotropic responsiveness to isoproterenol of hearts from spontaneously hypertensive rats during development.

The characteristics of the inotropic responses to isoproterenol (Iso) were investigated in isolated hearts from embryonic normotensive (NT) and spontaneously hypertensive (SH) Wistar-Kyoto rats at 14, 16, 18 and 20 days of gestation and from rats 3 and 10 weeks after birth and in ventricular strips prepared from hearts of newborn and 1-week-old rats. With rates of all preparations maintained constant by electrical stimulation, concentration and age dependent increases in contractility in response to Iso, capable of being blocked by propranolol, were observed. In embryonic hearts, irrespective of Iso concentration or embryonic age, similar effects were observed in hearts from NT and SH animals.

Adrenergic inotropic responsiveness of embryonic chick and rat hearts.

Rates of isolated embryonic chick hearts (ECH) and embryonic rat hearts (ERH) of various ages were maintained constant by field stimulation and the characteristics of their inotropic responses to isoproterenol (Iso) were investigated. Exposure to Iso produced concentration, age, species and calcium dependent increases in contractility that were prevented by propranolol (3x10(-6) M). The slopes of the linear portions of the concentration-response curves increased with age (14-20 days) in the ERH, the maximal slope and inotropic effect being observed in the 18-day-old heart, whereas they decreased with age (3-7 days) in the ECH, the minimal slope but maximal inotropic effect being observed in the 5-day-old heart.

Norepinephrine- and isoproterenol- induced changes in cardiac contractility and cyclic adenosine 3':5' -monophosphate levels during early development of the embryonic chick.

Changes in contractility and cyclic adenosine 3':5'-monophosphate (cAMP) levels in response to norepinephrine and isoproterenol were monitored in isolated 4-day-old (noninnervated) and 7-day-old (innervated) embryonic hearts to determine whether a relationship between beta adrenergic receptor, adenylate cyclase and altered cardiac function is established at a very early stage in embryonic development before innervation takes place. Norepinephrine and isoproterenol promoted rapid time- and dose-dependent rises in cAMP levels which were greater in the 4-day-old hearts. These increases paralleled observed functional alterations within a specific range of drug concentrations and time.