Compounds of formula (I), or pharmaceutically acceptable derivatives thereof, wherein: Het represents 2-pyridinyl or 2-pyrimidinyl; R.sup.1 represents H, C.sub.1-3 alkyl or a nitrogen-containing heterocyclic ring having 5 or 6 ring atoms; R.sup.2 represents H, benzyl or C.sub.1-3 alkyl; and R.sup.3 represents H, methyl, methoxy or chloro; are useful for treating anxiety, cardiovascular disease (including angina, atherosclerosis, hypertension, heart failure, edema, hypernatremia), dysmenorrhoea (primary and secondary), endometriosis, emesis (motion sickness), intrauterine growth retardation, inflammation (including rheumatoid arthritis), mittlesmerchz, preclampsia, premature ejaculation, premature (preterm) labor and Raynaud's disease.