**4. Correlation of parathyroid hormone and certain medical conditions**

The higher incidence of certain medical conditions that have been observed in patients with high levels of plasma PTH has raised the suspicion of a possible role of PTH in the development of these conditions whether directly or indirectly. The indirect action is represented by alteration of plasma calcium concentration in form of hypercalcemia or hypocalcemia with their known impact on the function of various body organs. The direct action of PTH is related to its ability to bind to a G-protein-coupled receptor (PTH1R) leading to its activation with subsequent downstream activation of adenylyl cyclase and protein kinase A pathway or phospholipase C/protein kinase C (PKC) pathway according to the target organ [11]. This sequence of events when occurs within the cardiomyocytes will trigger further steps that end with excessive growth of cardiomyocytes and left ventricular hypertrophy [12]. The prevalence of hypertension in patients with primary hyperparathyroidism is extremely high reaching 40–60% [13]. Various mechanisms have been suggested for this correlation such as activation protein kinase C, exaggerated cardiovascular reactivity to norepinephrine, amplified effects of the reninangiotensin system and many others [14]. Furthermore, altered glucose metabolism and even diabetes have been reported in patients with high plasma PTH concentration due to inhibition of insulin signaling in adipocytes via adenylate cyclase and phosphorylation of IRS-1 on serine 307 [15]. Approximately 8–22% of patients with primary hyperparathyroidism have type 2 diabetes mellitus and around 1% of patients with type 2 diabetes have primary hyperparathyroidism [16]. Although rare, acute pancreatitis has been as an initial presentation in patients with high plasma PTH levels due to a parathyroid gland tumor [17]. PTH has been correlated with metabolic syndrome, hyperlipidemia and coronary artery disease by many clinical studies [18–20]. For all this evidence, estimation of plasma PTH concentration should be a central step in the plan of management of many critical and highly prevalent medical conditions.
