Effects of L-dopa on plasma levels of parathyroid hormone in calves.

After oral administration of l-dihydroxyphenylalanine (L-dopa) to calves, plasma concentrations of L-dopa, dopamine, norepinephrine and parathyroid hormone increased whereas prolactin and calcium decreased while epinephrine remained unchanged. The decrease of prolactin presumably occurred as a consequence of the conversion of L-dopa to dopamine (in the hypothalamus), whereas the increase in parathyroid hormone was caused by hypocalcemia, by elevated dopamine and possibly by norepinephrine.