Postnatal changes in receptor-mediated rabbit gastric smooth muscle relaxation

Area of Science:

• Gastroenterology
• Pharmacology
• Developmental Physiology

Background:

• Understanding the mediators of gastric smooth muscle relaxation is crucial for comprehending gastric motility.
• Age-dependent changes in tissue response can significantly influence physiological functions during development.

Purpose of the Study:

• To identify the specific mediators responsible for relaxation in rabbit proximal gastric circular smooth muscle.
• To investigate how the tissue's response to these mediators changes with age, particularly during postnatal development.

Main Methods:

• Experiments were conducted on gastric muscle strips from newborn and weanling rabbits.
• Muscle strips were pre-contracted with bethanechol and then exposed to vasoactive intestinal peptide (VIP), adenosine, or norepinephrine.
• The effects of these substances on muscle relaxation and contraction were measured, along with the influence of receptor antagonists like phentolamine and propranolol.

Main Results:

• VIP, adenosine, and norepinephrine induced relaxation in a concentration-dependent manner, independent of tetrodotoxin.
• VIP's relaxation efficacy decreased significantly with age, while adenosine remained fully effective in both age groups.
• Norepinephrine initially caused relaxation in newborns but induced contraction in weanlings, mediated by alpha-adrenergic receptors, with a persistent beta-adrenergic relaxation component.

Conclusions:

• VIP, adenosine, and norepinephrine are key mediators of relaxation in rabbit gastric smooth muscle.
• Age-dependent shifts in VIP efficacy and the emergence of alpha-adrenergic contraction alongside beta-adrenergic relaxation in response to norepinephrine occur early in postnatal life.
• These age-related changes in mediator response likely contribute to the maturation of gastric motility.