Sex differences of neonatal bladder phasic contractile activity

In previous studies we showed that in vitro preparations of whole urinary bladders (UB) obtained from neonatal rats during the first three postnatal weeks exhibited large amplitude phasic contractions (PCs) that were enhanced by electrical stimulation of intramural nerves. The present experiments revealed that this type of phasic bladder activity occurs at different frequencies and exhibits different responses to pharmacological agents in UB preparations from two‐three week old male (M) and female (F) Sprague‐Dawley rats. While the amplitudes of the PCs (avg: 7 cmH2O) were similar in M and F rats the frequency of the PCs were almost two fold greater in F (5/min) than in M (3/min). Application of the muscarinic agonist (oxotremorine‐M, 0.05 uM) elicited a larger increase (2 fold) in the amplitude of the PCs in M versus F but did not change the frequency in either M or F. However the muscarinic antagonist, atropine methyl nitrate (5 uM) reduced the amplitude of PCs (34% decrease) in M but not in F without changing the frequency of the PCs. These results indicate that the amplitude of the basal phasic activity of M but not F neonatal rat bladders is facilitated by tonic activation of a muscarinic cholinergic mechanism. On the other hand F neonatal bladders exhibit a higher pacemaker activity than M bladders that is independent of muscarinic receptor activation. Support: NIH grants DK 49430 and DK 65759.