VI effects markedly attenuate V2 effects of AVP on urea transporter (UT) mRNA level in thin descending limb and initial inner medullary collecting duct

The mRNA level of short (S-) and long (L-) UT2 transcripts (tubular), and that of UT11 (vascular) were measured in Brattleboro rats with diabetes insipidus (DI), treated for 5 days with either AVP (5 μg/day) or the V2 agonist dDAVP (0.25 μg/day), and in control (Co) DI rats. Specific mRNAs were quantified by Northern analysis of 7 μg total RNA extracted from superficial and deep inner stripe (s-IS and d-IS) of outer medulla, and from base and tip of inner medulla (IM). mRNA levels are expressed as arbitrary units of density. Results are means ± SEM (n =3 ). AVP and dDAVP induced similar Uosm (2167 ± 79 for AVP, and 1831 ± 106 for dDAVP, vs 220 ± 45 mOsm / kg H₂O for Co). Both hormones induced similar decrease in UT11 in whole IM, and similar increase in S-UT2 in s- and d-IS. Long UT2 of tip-IM was unchanged. However AVP induced much less increase in the following parameters than did dDAVP: S-UT2 in d-IS S-UT2 in base IM L-UT2 in base IM Co Exp Co Exp Co Exp AVP: 91 ± 21 247 ± 22* 21 ± 2 185 ± 38*65 ± 11 108 ± 33 dDAVP: 183 ± 9 # 2093 ± 130*# 19 ± 5 1139 ± 148*# 42 ± 8 803 ± 11*#*: p < 0.05 or less vs Co; #: p < 0.05 or less vs AVP (Student's t test) AVP and dDAVP induce similar changes in UT11 mRNA expression. In contrast, the attenuated effect of AVP vs dDAVP on expression of UT in thin descending limb (S-UT2), and in initial IM collecting duct (L-UT2 in base IM), likely results from blunted V2 effect by V1 effect of AVP.