1. Fundamentals of Pharmacology for Veterinary Technicians
Chapter 10
Hormonal and Reproductive Drugs
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2. Basic Anatomy and Physiology
The endocrine system is composed of ductless glands that secrete chemical messengers called hormones into the blood
Hormones are chemical substances produced by cells in one part of the body and transported to another part of the body where they influence cellular activity
The endocrine system is controlled by a feedback mechanism that includes the hypothalamus, pituitary gland, and the other endocrine glands
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3. Basic Anatomy and Physiology
Two types of feedback loops are involved in regulating the endocrine system
Feedback loops may be either negative or positive
Negative feedback loops are more common and work in response to low or high levels of hormone in the body
Positive feedback loops occur when hormone levels continue to rise in response to stimuli
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4. Basic Anatomy and Physiology
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5. Pituitary Gland Hormones
The pituitary gland is divided into two parts: anterior (cranial) and posterior (caudal)
Anterior pituitary hormones used in veterinary practice include:
Thyroid stimulating hormone (TSH)
Adrenocorticotropic hormone (ACTH)
Follicle stimulating hormone (FSH)
Luteinizing hormone (LH)
Growth hormone (GH)
Posterior pituitary hormones used in veterinary practice include:
Antidiuretic hormone (ADH)
Oxytocin
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6. Anterior Pituitary Gland Hormones
TSH is used in the diagnosis of primary hypothyroidism
ACTH is used to stimulate the adrenal cortex to secrete corticosteroids in the diagnosis of adrenal cortex disease
FSH and LH (see reproductive section)
GH is used to increase growth rate and feed use efficiency in livestock and increase milk production in dairy cows
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7. Posterior Pituitary Gland Hormones
ADH is used to treat diabetes insipidus (disease characterized by the inability to concentrate urine due to insufficient amounts of ADH)
Oxytocin is used to aid in uterine contraction and induce labor in animals at term, expel the placenta, induce milk letdown, and as an adjunct therapy for animals with open pyometra
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8. Hormones of the Pancreas
The pancreas secretes two hormones that help regulate blood glucose
Insulin responds to a rise in blood glucose and promotes the uptake and use of glucose for energy in cells
Glucagon increases blood glucose levels by promoting the breakdown of glycogen into glucose
Diabetes mellitus is a disease of fat, carbohydrate, and protein metabolism caused by lack of or inefficient use of insulin
Treated both with diet changes and medically
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Insulin
Insulin is used to treat diabetes mellitus by keeping blood glucose in the proper range
Sources of insulin include pork, synthetic, and recombinant forms
Onset and duration of insulin action are controlled by modifying the regular insulin structure
Short-acting is used for initial treatment of diabetic ketoacidosis and keep blood glucose stable (regular crystalline insulin, semilente)
Intermediate-acting is used to control blood glucose in uncomplicated cases of diabetes mellitus (NPH and lente)
Long-acting is used to control blood glucose for longer periods of time, especially in cats (protamine zinc insulin and ultralente)
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10. Oral Hypoglycemic Agents
Oral hypoglycemic agents have been used with some success in animals
Work by stimulating pancreatic beta cells to secrete insulin; therefore some pancreatic function is needed
Has been more successful in cats
An example of an oral hypoglycemic agent is glipizide
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Thyroid Hormones
The thyroid gland secretes two hormones involved in metabolism:
Thyroxine or T4
Triiodothyronine or T3
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12. Diseases Involving Thyroid Hormones
Hypothyroidism is characterized by a deficiency of thyroid hormone
Signs of hypothyroidism include decreased coat and hair luster, weight gain, listlessness, intolerance to cold, and reproductive failure
Diagnosed by measuring serum total T4 and T3 or by a thyroid stimulation test or by the thyrotropin releasing hormone response test
Hypothyroid animals are treated with thyroid replacement therapy
levothyroxine (T4)
liothyronine (T3)
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13. Diseases Involving Thyroid Hormones
Hyperthyroidism is characterized by an increased production of thyroid hormone
Signs of hyperthyroidism include increased thirst, weight loss, increased stool production, restlessness, and tachycardia
Diagnosed by measuring serum total T4 and T3
Hyperthyroid animals are treated with antithyroid drugs or surgical removal
Radioactive isotopes of iodine (I-131) destroy the thyroid gland
Methimazole: interferes with the incorporation of iodine in the molecules of T4 and T3
Propylthiouracil (PTU): interferes with the conversion of T4 to T3
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14. Adrenal Cortex Hormones
The adrenal cortex is the outer part of the adrenal gland
The hypothalamus regulates the adrenal cortex by secreting releasing hormones for ACTH, which stimulates the adrenal cortex
Hormones produced by the adrenal cortex include mineralocorticoids (aldosterone; covered in chapter 12) and glucocorticoids (cortisol)
Glucocorticoids regulate nutrient levels in blood (increase blood glucose levels)
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15. Diseases of Adrenal Cortex Hormones
Adrenocortical insufficiency (Addison’s disease) is a progressive condition associated with adrenal atrophy
Result is a deficient production of corticosteroids and mineralocorticoids
Signs of this disease include lethargy, weakness, anorexia, vomiting, diarrhea, and PU/PD
Diagnosed by the ACTH stimulation test
Treatment involves a long-acting mineralocorticoid and corticosteroids
Desoxycorticosterone (DOCP): mineralocorticoid
Corticosteroids (Chapter 16)
Fludrocortisone: both glucocorticoid and mineralocorticoid activity
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16. Diseases of Adrenal Cortex Hormones
Hyperadrenocorticism (Cushing’s disease) is characterized by excessive glucocorticoid production due to prolonged administration of adrenocortical hormones, adrenocortical tumors, or pituitary disorders
Signs: PU/PD, hair loss, pendulous abdomen
Diagnosed by the ACTH stimulation test or low-dose dexamethosone suppression test
Treatment involves destroying part of the adrenal cortex
Mitotane (o, p’-DDD)
Ketoconazole: antifungal that blocks the enzymes needed to produce steroid compounds
Selegiline: monoamine oxidase inhibitor
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17. Basic Anatomy and Physiology
Reproductive system is responsible for the process of producing offspring
Males
Testes, epididymis, ductus deferens, accessory sex glands, urethra, penis
Sperm are produced in the seminiferous tubules of the testes
Females
Ovaries, uterine tubes, uterus, cervix, vagina, and vulva
Ova are produced in the Graafian follicle of the ovary
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18. Drugs Affecting Reproduction
Androgens are male hormones
Testosterone:
Made in the interstitial cells of the testes
Used to treat conditions such as infertility and hypogonadism, produce estrus detectors, and for testosterone-responsive urinary incontinence in dogs
Examples:
Testosterone cypionate in oil
Testosterone enanthate in oil
Testosterone propionate in oil
Danazol
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19. Drugs Affecting Reproduction
Androgens are male hormones (cont.)
Mibolerone:
Blocks the release of LH from the anterior pituitary gland; therefore the follicle does not fully develop
Used to prevent estrus in adult female dogs and the treatment of false pregnancies
Zinc gluconate neutralized by arginine:
Nonsurgical neutering drug
Chemical sterilant approved for use in 3- to 10-month-old male dogs
Used as an intratesticular injection
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20. Drugs Affecting Reproduction
Female hormones
Estrogen:
Promotes female sex characteristics and stimulates and maintains the reproductive tract
Synthetic estrogens are used in dogs to prevent implantation of fertilized ova and to correct urinary incontinence, vaginitis, and dermatitis
Synthetic estrogens are used in cattle to treat persistent corpus luteum, aid in expulsion of retained placentas and mummified feti, and to promote weight gain
Synthetic estrogens are used in horses to induce estrus in the nonbreeding season
See further information under the growth promotant section
Examples:
Estradiol cypionate
Diethylstilbestrol
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21. Drugs Affecting Reproduction
Female hormones (cont.)
Progesterone:
Decreases uterine activity when a female is in estrus or pregnant
Progestins (a group of compounds similar in effect to progesterone) are used in dogs to block estrus
Progestins are used in cattle to synchronize breeding and birth cycles
Progestins may be used to treat behavior problems and some forms of dermatitis
Examples include:
Megestrol acetate
Medroxyprogesterone acetate
Altrenogest
Progesterone
Melengestrol
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22. Drugs Affecting Reproduction
Female hormones (cont.)
Prostaglandins:
In the reproductive system, prostaglandin F2α causes lysis of the corpus luteum, which initiates a new estrus cycle
In small animals, prostaglandins are used to treat pyometra, cause abortion, and induce parturition
In cattle, prostaglandins are used for estrus synchronization and inducing uterine contractions to facilitate emptying of the uterus (pus or fetus)
In horses, prostaglandins are used for estrus synchronization
Examples:
Dinoprost tromethamine
Fluprostenol
Cloprostenol sodium
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Gonadotropins
Gonadotropins are hormones that stimulate the gonads
These drugs cause the release of LH and FSH or simulate their activity
Gonadotropins include LH (simulated by the use of hCG), FSH (simulated by the use of PMSG), and GnRH (made synthetically)
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Gonadotropins
Human chorionic gonadotropin (hCG) is used to treat cystic ovaries in cattle, to detect cryptorchidism in dogs, to get infertile bitches to cycle, and to make breeding mares ovulate
Pregnant mare serum gonadotropin (PMSG) is used to produce estrus and ovulation in horses and as a follicle stimulant in many species
Gonadorelin (GnRH) is used to treat follicular cysts in cattle, for estrus synchronization in cattle, and to induce estrus in small animals
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Growth Promotants
Always check label to make sure growth promotants can be used in the species you are working with
Hormonal growth promotants
Estradiol (tablet or implant used in ruminants)
Testosterone (used in combination with estradiol to slow the release rate of estradiol)
Progesterone (used in combination with estradiol)
Synthetic hormones
TBA (works like testosterone)
MGA (works like progesterone)
Zeranol (analog of plant estrogen)
Anabolic steroids
Stanozolol
Boldenone undecylenate
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