Ritodrine: An adrenergic beta-2 agonist used to control PREMATURE LABOR.Isoxsuprine: A beta-adrenergic agonist that causes direct relaxation of uterine and vascular smooth muscle. Its vasodilating actions are greater on the arteries supplying skeletal muscle than on those supplying skin. It is used in the treatment of peripheral vascular disease and in premature labor.Tocolytic Agents: Drugs that prevent preterm labor and immature birth by suppressing uterine contractions (TOCOLYSIS). Agents used to delay premature uterine activity include magnesium sulfate, beta-mimetics, oxytocin antagonists, calcium channel inhibitors, and adrenergic beta-receptor agonists. The use of intravenous alcohol as a tocolytic is now obsolete.Mephentermine: A sympathomimetic agent with specificity for alpha-1 adrenergic receptors. It is used to maintain BLOOD PRESSURE in hypotensive states such as following SPINAL ANESTHESIA.Uterine Contraction: Contraction of the UTERINE MUSCLE.TartratesEphedrine: A phenethylamine found in EPHEDRA SINICA. PSEUDOEPHEDRINE is an isomer. It is an alpha- and beta-adrenergic agonist that may also enhance release of norepinephrine. It has been used for asthma, heart failure, rhinitis, and urinary incontinence, and for its central nervous system stimulatory effects in the treatment of narcolepsy and depression. It has become less extensively used with the advent of more selective agonists.Propanolamines: AMINO ALCOHOLS containing the propanolamine (NH2CH2CHOHCH2) group and its derivatives.Obstetric Labor, Premature: Onset of OBSTETRIC LABOR before term (TERM BIRTH) but usually after the FETUS has become viable. In humans, it occurs sometime during the 29th through 38th week of PREGNANCY. TOCOLYSIS inhibits premature labor and can prevent the BIRTH of premature infants (INFANT, PREMATURE).