Urinary oxytocin secretion after pituitary surgery, early arginine vasopressin deficiency and syndrome of inappropriate antidiuresis

Transient arginine vasopressin deficiency (AVP-D), previously called diabetes insipidus, is a well-known complication of transsphenoidal pituitary surgery (TPS) with no definite predictive biomarker to date making it difficult to anticipate. While oxytocin (OXT) was previously suggested as a possible biomarker to predict syndrome of inappropriate diuresis (SIAD)-related hyponatraemia after TPS, its secretion in patients presenting with AVP-D remains poorly understood. We therefore hypothesized that OXT might present a different secretion in the case of AVP-D which would support its potential as an early biomarker of AVP-D. Moreover, we hypothesized that abnormal secretion of OXT might occur later on, notably with SIAD.

We measured the urinary output of OXT in 67 consecutive patients subjected to TPS and compared the values of oxytocin between time-points and OXT ratio between groups. The primary endpoint of our study was to identify a difference in urinary OXT excretion in patients suffering from AVP-D compared to patients remaining normonatraemic. As a secondary endpoint, we compared the evolution of OXT secretion after the diagnosis of AVP-D in both groups, comparing the patients that later developed SIAD with the ones that did not.

Patients developing AVP-D showed a delay in the increase of OXT secretion after TPS as shown by a significantly lower ratio of OXT between the first postoperative day and the day of surgery (0.88 VS 1.68, p = 0.0162, IC:0.2979–0.2642) but a significantly higher ratio of OXT between the fourth and the first postoperative days (1.17 VS 0.53, p = 0.0006, IC:−2.109–0.6092). Moreover, normonatraemic patients that did not show normalization of OXT levels at day 4 after surgery tended to develop SIAD later on.

Taken together, these results show for the first time that OXT release might help predict AVP-D after TPS and differentiate it from other pathologies of water-sodium balance.