Vasopressin is a nonapeptide, and its analogues are various modifications of that same basic molecular structure, used to change the pharmacokinetics and receptor selectivity of the end product. Terlipressin is a prodrug for lysine vasopressin which has a higher selectivity for V1 receptors, making it an almost pure vasopressor, and desmopressin (DDAVP) has a higher selectivity for V2 receptors, making it a more pure antidiuretic.
Numerous chemically diverse classes of oral hypoglycemic agents with various mechanisms of action exist, including biguanides, sulfonylureas, α-glucosidase inhibitors, meglitinides, thiazolidinediones, DPP-4 inhibitors, and SGLT-2 blockers. Unsurprisingly, for the majority of these (with some exceptions), hypoglycaemia is the most clinically important adverse effect.
Regular human insulin (eg. Actrapid) is an exact duplicate analog of the human peptide hormone, consisting of 51 amino acids. Other insulin variants modify the normal molecule to adjust the self-association behaviour of the drug, leading to longer or shorter absorption from the subcutaneous depot.
Different corticosteroid drugs tend to be used for different conditions because of some peculiarities in their pharmacokinetics and pharmacodynamics. For example, methylprednisolone penetrates best into the lung, whereas dexamethasone can cross the blood-brain barrier more easily mainly because it is less protein-bound. These differences in pharmacology dictate the specific use case scenarios for corticosteroids.
Corticosteroids have numerous effects, some often described as "adverse", but their undeniable safety needs to be highlighted, as there are very few endogenous substances for which, following the administration of an exogenous dose one hundred times the normal level, nothing serious happens.
Corticosteroids are all very similar chemically. They are highly lipid soluble molecules which undergo extensive hepatic metabolism and which are highly protein-bound (mainly to albumin, but also partly to specific chaperone globulins in the plasma). Their half-lives range from 60 minutes (hydrocortisone) to 11 hours (betamethasone), but the duration of effect is not related to this timeframe, as most of their effects are genomic and manifest in terms of changes in protein synthesis over many hours and days.
Thyroid hormones are iodinated tyrosine derivatives with pleiotropic effects. Levothyroxine is identical to the endogenous T4, and is metabolised into triiodothyronine (which is also available as an IV infusion). These drugs have multiple effects on metabolism, cardiovascular function, neurological function, and gastrointestinal activity, which can be broadly summarised as "more of everything".
Calcium homeostasis is regulated by three main hormones: parathyroid hormone (PTH), calcitriol, and calcitonin. PTH and calcitriol work to increase plasma calcium by increasing its absorption from the intestine and bone, and by resisting its loss in the renal tubule. Calcitonin, on the other hand, defends against hypercalcemia by inhibiting bone resorption and encouraging renal elimination.
Adrenal hormones include cortisol, aldosterone, androgens, and catecholamines. Each hormone is secreted from structurally and functionally distinct zones of the adrenal gland. The synthesis of steroid hormones occurs on demand in the adrenal cortex, whereas catecholamines are constantly being synthesised and stored in chromaffin granules inside cells of the adrenal medulla. The stimuli for their release can be broadly summarised as "stress".
Renal hormones include erythropoietin, renin, thrombopoietin and urodilatin. The kidney also has numerous other endocrine functions, briefly summarised in this chapter, such as the modification of Vitamin D and the clearance of circulating hormones from the blood.
Thyroid hormones are a major regulator of metabolism and thermogenesis, besides being essential for development. Their actions are exerted by binding to nuclear receptors which regulate gene transcription, and are therefore slow to manifest.
The hypothalamus and pituitary are small CNS endocrine organs that are involved in the regulation of numerous processes, among them the autonomic nervous system, temperature, body water volume, reproductive function, emotion, metabolic rate, satiety, and stress responses.
Glucose release and storage are regulated by the balance between the actions of insulin and glucagon. Insulin promotes glucose uptake and storage, whereas glucagon promotes glucose release from stores and glucose synthesis from amino acids and lactate. The pancreatic β-cells and α-cells are the main sensory organ for the detection of glucose, with the hypothalamus playing a minor role in the control of satiety and autonomic responses to hyper and hypoglycaemia.
Somatostatin is a counter-secretory hormone which acts as the antagonist for the secretory activity of most endocrine and exocrine glands. It is secreted from numerous tissue sources, including the intestine (65%) brain (25%) and pancreas (5%). The main mechanism of effect is mediated by the inhibition of adenylyl cyclase, which decreases cAMP concentrations and inhibits exocytosis.