Description
DRUGS ACTING ON ENDOCRINE SYSTEM
11.1.1. Introduction
The endocrine system consists of glands secreting hormones essential for
maintenance of homeostasis throughout the body. Hormones are chemical
messengers that act to control and coordinate different fu nctions of tissues and
organs.
Various body activities like growth and development and metabolism are also
regulated by hormones. Each hormone is secreted from a particular gland and is
distributed to the target tissues via blood.
Endocrine glands are ductless glands, thus release their products directly into
the bloodstream, and are carried to their target cells. On the other hand, exocrine
glands secrete their products (excluding hormones and other chemical
messengers) into the ducts, which are then transported to the bloodstream.
The endocrine system comprises of all the endocrine glands of the body.
Pituitary, pineal, thyroid, adrenal, pancreas, parathyroid, thymus, and
gonads (testis in males and ovary in females) are the endocrine glands found in
humans.
These glands work in conjunction with the nervous system, and therefore this
complex of two systems is referred to as the neuroendocrine system . This
system controls and coordinates various functions of the body, maintaining
homeostasis (constancy of body fluids) within the body. The term
neuroendocrinology defines the study of endocrine system in combination with
the nervous system.
11.1.2. Hormones
The word hormone has originated from a Greek hormaein which means to
impel. Thus, hormone is a substance which is secreted by specialised cells and
transported to a distant site to exert its action upon specific tissues. Hormones are
synthesised and discharged by endocrine glands directly into the blood
circulation without the intervention of a duct , therefore known as ductless
glands.
If a hormone acts on other endocrine gland or tissue, it just stimulates or inhibits its function.
Major Hormones Secreted by the Endocrine GlandsTable 11.1 enlists the different endocrine glands, the hormones they release, t he target tissues, and the major functions of hormones:Table 11.1: Functions of HormonesEndocrineGlandsHormones Released Chemical ClassesTarget Tissues or OrgansMajor Functions of HormonesHypothalamus Hypothalamic releasing and inhibiting hormonesPeptide Anterior pituitaryRegulate anterior pituitary hormones.Posteriorpituitaryi) Antidiuretic Hormone (ADH or vasopressin)Peptide Kidneys Stimulates water reabsorption by kidneys.ii) Oxytocin Peptide Uterus and mammary glandsStimulates uterine muscle contractions and release milk by mammary glands.Anteriorpituitaryi) Thyroid Stimulating Hormone (TSH)ii) Adrenocorticotropic Hormone (ACTH)iii) Gonadotropins (FSH, LH)iv) Prolactin (PRL)GlycoproteinPeptideGlycoproteinProteinThyroidAdrenal cortexGonadsMammary glandsSoft tissue, and bonesStimulates thyroid gland.Stimulates adrenal cortex.Produce egg, sperm, and sex hormones.Produces milk. Stimulates cell division, protein synthesis, and bone growth.v) Growth Hormone (GH)ProteinThyroid i) Thyroxine (T4) and Triiodothyronine (T3)Iodinated amino acidAll tissues Increase metabolic rate, regulate growth and development.ii) Calcitonin Peptide Bones, kidneys, and intestinesLowers blood calcium level.Parathyroid Parathormone (PTH) Peptide Bones, kidneys, and intestinesRaises blood calcium level.Adrenal cortexi) Glucocorticoids (cortisol)Steroid All tissues Raise blood glucose level, and stimulate protein breakdown.ii) Mineralocorticoids (aldosterone)Steroid Kidneys Re-absorb sodium and excrete potassium.AdrenalmedullaEpinephrine and norepinephrineModified amino acidCardiac and other musclesReleased in emergency situations, raise blood glucose level, and bring on “fight or flight’ response.Pancreas i) Insulin Protein Liver, muscles, and adipose tissuesLiver, skeletal Lowers blood glucose levels and promotes formation of glycogen.
The ring A has the flexibility to take boat conformation; however it also has chair
conformation. The r ing D is slightly puckered. The conformations of C―H,
C―CH3 and C―OH bonds are observed. A bond may be axial (a), parallel to the
axis of symmetry of the ring, or equatorial (e), radiating in the plane of the ring.
The 5- and 5 -cholestan-3-ol vary with respect to the ir configurations at
position 5. In the former, the rings A/B are trans fused and in the latter the rings
A/B are cis fused.
Due to this difference the conformationsget disturbed at different ring A positions,
and this can be seen at positions 3, 5, and 10. The hydroxyl groups at position 3 in
both have the same configuration (), but conformationally the 3-OH are equa-
torial and 3-H are axial in 5-cholestan-3-ol, while the condition is just the
reverse in 5-cholestan-3-ol. In 5-cholestan-3-ol, 5-H and 10-CH3 are axial
in relation to rings A and B; while in 5-cholestan-3-ol, 5-H is axial with respect
to ring A and equatorial with respect to ring B; in the same molecule, 10-CH3 is
equatorial with respect to ring A and axial with respect to ring B. Conformational
analysis provides a description of3-D forms of the steroids.
11.2.4. Biosynthesis of Steroids
The steroids secreted by the endocrine glands (such as ovaries, testes and adrenal
glands) are released d irectly in the blood circulation, and are termed steroidal
hormones. These hormones have many activities and their absence may prove to
be fatal. The major classes of steroidal hormones are given below:
1) Female Sex Hormones : The major hormones are oestrogens and
progesterones.
2) Male Sex Hormones: The major hormone is androgens.
3) Adrenocorticoids: The major hormones are glucocorticoids and
mineralocorticoids.
Subject:- Medicinal chemistry 2
Semester:- Sem 5
Course:- Bachelor of pharmacy
