Oxytocics reverse the tocolytic effect of glyceryl trinitrate on the human uterus.
OBJECTIVE
To investigate the effect of glyceryl trinitrate on isolated human pregnant uterine strips and whether the uterine relaxation induced by glyceryl trinitrate could be reversed by oxytocics used in current clinical practice.


METHODS
In vitro pharmacological study.


METHODS
Department of Obstetrics & Gynaecology, National University of Singapore, National University Hospital.


METHODS
Eighteen women who delivered by caesarean section at term.


METHODS
Myometrial strips were preloaded with an initial tension of 1.5g in organ baths containing Krebs-Henseleit solution which was aerated with oxygen in 5% carbon dioxide and maintained at 37 degrees C, pH 7.4. The effect of glyceryl trinitrate was studied in strips displaying regular spontaneous contractions. The ability of oxytocin, ergometrine or prostaglandin F2alpha to stimulate uterine contractions was assessed in strips where uterine activity was significantly inhibited by glyceryl trinitrate.


RESULTS
Glyceryl trinitrate reduced the amplitude and frequency of spontaneous uterine contractions in a concentration-dependent manner, although the sensitivity of the myometrial strips varied considerably from one specimen to another. The concentration of glyceryl trinitrate producing complete inhibition of myometrial contractions ranged from 44-705 microM. In the presence of glyceryl trinitrate which markedly depressed spontaneous contractions, oxytocin (20 mU/mL), ergometrine (6.15 microM) and prostaglandin F2alpha (6.15 microM) were capable of reversing the uterine activity to either higher than or the untreated level of contractility.


CONCLUSIONS
This study demonstrates that glyceryl trinitrate is a potent uterine relaxant in vitro and that the tocolytic effect could be reversed with ease by oxytocics.
Department of Obstetrics and Gynaecology, National University Hospital, Singapore.
L C
LC
Lau
P G
PG
Adaikan
S
S
Arulkumaran
S C
SC
Ng
D015237:Dinoprost / Q000494:pharmacology; D004874:Ergonovine / Q000494:pharmacology; D005260:Female; D006801:Humans; D009215:Myometrium / Q000187:drug effects*; D005996:Nitroglycerin / Q000494:pharmacology*; D010120:Oxytocics / Q000494:pharmacology*; D010121:Oxytocin / Q000494:pharmacology; D011247:Pregnancy; D014590:Uterine Contraction / Q000187:drug effects*; D014665:Vasodilator Agents / Q000494:pharmacology*
D010120:Oxytocics; D014665:Vasodilator Agents; D010121:Oxytocin; D015237:Dinoprost; D005996:Nitroglycerin; D004874:Ergonovine