Previous studies in rat kidneys have demonstrated that oscillations in the proximal intratubular pressure are a prominent feature of the tubulo-glomerular feedback mechanism (TGF) operating during free flow conditions. The purpose of the present study was to investigate whether a subpopulation of synchronized, interacting nephrons could be detected. In group A nephrons, i.e., nephrons with a high probability of having their afferent arterioles arising from the same interlobular artery, 29 out of 33 pairs of nephrons were found to show synchronized pressure oscillations. In group B nephrons, not expected to have this common origin of their afferent arterioles, only 1 out of 23 pairs was found to be synchronized. The standard deviation of the frequency differences was 0.063 cycles per minute in group A nephron pairs and 0.202 cycles per minute in group B pairs (p less than 0.05), showing the greater homogeneity in frequency in group A. Furthermore, nephrons having synchronized pressure oscillations were found to interact with each other. Thus, perturbation of the proximal tubular pressure oscillations in one nephron by loop microperfusion affected the amplitude of the pressure oscillations in the non-perfused nephron; and reactivation of pressure oscillations in one nephron was followed by reactivation of oscillations in the non-perfused nephron. Thus, the present results show that there exists a well defined subpopulation of nephrons, in which the TGF-mediated proximal pressure oscillations are synchronized. This synchronization is a result of interaction between the different nephrons.(ABSTRACT TRUNCATED AT 250 WORDS)