J. Magraner et al., CHARACTERIZATION OF TACHYKININ RECEPTORS IN THE UTERUS OF THE ESTROGEN-PRIMED RAT, British Journal of Pharmacology, 123(2), 1998, pp. 259-268
1 The aim of our study was to characterize the tachykinin receptor pop
ulation in the oestrogen-primed rat uterus. For this purpose, we inves
tigated the receptor type(s) responsible for tachykinin-induced contra
ction of longitudinally-arranged smooth muscle layer. The effects of s
ubstance P (SP), neurokinin A (NKA), neurokinin B (NKB) and several of
their analogues with well-defined selectivities for tachykinin NK1, N
K2 and NK3 receptors were studied and their inhibition by the selectiv
e nonpeptide tachykinin receptor antagonists -3-yl]ethyl)-4-phenyl-1-a
zoniabicyclo[2.2.2]octane chloride (SR 140333, NK1-selective), lpiperi
dino)-2-(3,4-dichlorophenyl)butyl]benzamide (SR 48968, NK2-selective)
and )propyl)-4-phenylpiperidin-4-yl)-N-methylacetamide (SR 142801, NK3
-selective) was evaluated. Additionally, expression of tachykinin rece
ptor mRNA was examined by using the reverse transcription-polymerase c
hain reaction (RT-PCR). 2 SP, NKA, [Nle(10)]-NKA(4 - 10), the analogue
with selectivity at the tachykinin NK2 receptor type, and NKB elicite
d concentration-dependent contractions of the rat uterus. The pD(2) va
lues were 5.95 +/- 0.19; 6.73 +/- 0.21; 7.53 +/- 0.12 and 5.76 +/- 0.2
1, respectively. The selective agonist for the tachykinin NK1 receptor
[Sar(9)Met(O-2)(11)]-SP produced a small phasic response in the nanom
olar concentration range. The selective tachykinin NK3 receptor agonis
t [MePhe(7)]-NKB failed to induce any significant contraction. 3 In th
e presence of the neutral endopeptidase inhibitor phosphoramidon (1 mu
M), the log concentration-response curves to exogenous tachykinins an
d their analogues were shifted significantly leftwards. The pot values
were 6.12 +/- 0.10, 8.04 +/- 0.07, 7.89 +/- 0.03 and 6.59 +/- 0.07 fo
r SP, NKA, [Nle(10)]-NKA(4 - 10) and NKB, respectively. In the presenc
e of phosphoramidon (1 mu M), [Sar(9)Met(O-2)(11)]-SP (1 nM - 0.3 mu M
) induced concentration-dependent contractions of increasing amplitude
when only one concentration of drug was applied to each uterine strip
and the pD(2) value was 7.61 +/- 0.89. [MePhe(7)]-NKB induced small,
inconsistent contractions and, therefore, a pot value could not be cal
culated. 4 In experiments performed in the presence of phosphoramidon
(1 mu M), SR 48968 (3 nM - 0.1 mu M) caused parallel and rightward shi
fts in the log concentration-response curves of NKA. The calculated pK
(B) value was 9.16 +/- 0.08 and the slope of the Schild regression was
1.28 +/- 0.24. SR 48968 (0.1 mu M) also antagonized responses to SP w
ith an apparent pK(B) value of 7.63 +/- 0.13. SR 48968 (0.1 mu M) inhi
bited contractions elicited by NKB (1 nM - 3 mu M) and [Nle(10)]-NKA(4
- 10) (0.1 nM - 3 mu M) but had no effect on the response evoked by [
Sar(9)Met(O-2)(11)]-SP (0.1 mu M). 5 SR 140333 (0.1 mu M) inhibited re
sponses to SP with an apparent pK(B) value of 7.19 +/- 0.22. This comp
ound did not significantly affect responses to NKA, [Nle(10)]-NKA(4 -
10) and NKB, but suppressed [Sar(9)Met(O-2)(11)]-SP (0.1 mu M)-induced
contraction. SR 142801 (0.1 mu M) had no effect on responses to natur
al tachykinins or their analogues. 6 Total RNA was extracted from some
of the uteri used in functional studies. RT-PCR assays revealed singl
e bands corresponding to the expected product sizes encoding cDNA for
tachykinin NK1 (587 base pairs) and NK2 receptors (491 base pairs) (n
= 6 different animals). A very low abundance transcript corresponding
to the 325 base pairs product expected for the tachykinin NK3 receptor
was detected. 7 The present data show that functionally active tachyk
inin NK1 and NK2 receptors are expressed in the oestrogen-primed rat u
terus. The NK2 receptor type seems to be the most important one involv
ed in the contractile responses elicited by tachykinins. NK3 receptors
are present in trace amounts and seem not to be involved in tachykini
n-induced contractions.