Arginine vasopressin is primarily recognized as an osmoregulatory hormone; however, its contribution to vascular tone and blood pressure regulation under basal and hypertensive conditions remains debated. This study examined the effects of vasopressin deficiency induced by neurointermediate pituitary lobectomy in Wistar and spontaneously hypertensive rats, compared with sham-operated controls. Water intake, urine output, plasma vasopressin and oxytocin levels, blood pressure, and heart rate were evaluated over time. Neurointermediate pituitary lobectomy produced transient diabetes insipidus followed by the restoration of water balance, while plasma vasopressin and oxytocin levels remained markedly reduced at 3- and 90-days post-surgery (p < 0.0001 vs. Sham). This deficiency was associated with sustained hypotension in Wistar rats (~27 mmHg; p < 0.05) and normalized systolic blood pressure in spontaneously hypertensive rats (~50 mmHg; p < 0.001). Acute and chronic vasopressin and oxytocin deficiency causes transient diabetes insipidus, persistent hypotension in normotensive rats, and attenuated hypertension in spontaneously hypertensive rats with unchanged heart rate, demonstrating that vasopressin plays a key role in regulating both basal and hypertensive blood pressure.