A mathematical model of prolactin secretion: Effects of dopamine and thyrotropin-releasing hormone

Prolactin (PRL) is secreted in a pulsatile manner by lactotroph cells in the anterior pituitary gland and displays a circadian rhythm as well as increases in response to stress, sexual intercourse, breast stimulation, and suckling. We propose a mathematical model of prolactin secretion which is mainly controlled by the inhibiting effect of dopamine (DA) and the stimulating effect of thyrotopin releasing hormone (TRH). By applying the singular perturbation technique, the conditions are derived under which our model exhibits a periodic solution corresponding to the normal secretory pattern of PRL which has been observed as a series of daily pulses, occurring every 2–3 hours. Numerical investigations also show that chaotic time series is admitted by our model which resembles irregular patterns observed in PRL concentration profiles of patients with microprolactinoma and macroprolactinoma. Explaining the conditions that delineate varying dynamic behavior in this nonlinear system in terms of the removal rates of the three state variables, the removal rate d1 of TRH seems to play the most important role in identifying different physiological conditions.